Combine juice, mustard, honey, salt and pepper in a small bowl and whisk together. Place onions and spinach in a large bowl. Add dressing and toss together. Top with blue cheese.

Interesting method

I don't want to ruin your meal, but I feel obligated to. The recipe you described is poison to your body. Please, please, do not eat that.

The reason fruits are found and eaten whole in nature is because the largest part of the fruits are fiber that act as a sponge that soaks up much of the fruit sugar, the fructose. If you consume fruit juice without the fiber from the whole fruit, the fructose instead ends up at your liver, where it will be stored as liver fat because the human body has no use for fructose. It is sweeter than table sugar and it is pure poison.

The human body needs amino acids and fatty acids for macro nutrients and a whole array of micro nutrients from animal derived food. What the human doesn't need are carbs and plant derived foods. Which is almost redundant to say because all plants contain a good amount of carbohydrates.

If you commit to a diet of plant based foods, you are on a diet of poison. The only thing worse than to not eat anything of nutritional value is to not eat anything of nutritional value and put poison into your stomach on top of it. Spinach is not healthy, no matter how much advertisements in cartoon format one may have watched with that ad character Popeye.
Spinach by itself is poison to the body, but if you also add dressings to salads and greens, you will make it even worse. Dressings are generally a form of oil or fat and the most common vitamins in most plants are vitamins that are fat soluble, which means that you only get the vitamins out of them if you add fat, like an oily dressing, to it. The problem with that is that fat soluble vitamins are all produced by the human body on its own in sufficient amount. The human body does not need a lot of it. And so if you eat any plant derived foods like a salad or spinach with these dressings, you end up feeding your body more vitamins than it can handle.

I would also be careful with honey. Honey is not honey. The composition of honey is different for each honey. The flowers that the nectar is taken from decide to a good portion how the honey ends up. And if bees take the nectar from the wrong flowers, and there are plenty of poisonous flowers, then these poisons end up in the honey as well. The amounts are so small that they largely do not affect such a big organism like a human immediately. But it will still over time damage your body. And if the honey has been around for too long, it will 'spoil', yes honey spoils, any honey no matter which will at some point grow hard and solid and long before the hardening begins the honey will produce toxic compounds like HMF.

The most common cause for overweight are diets with too much carbohydrates and greens and not enough animal food like fat, meat, eggs or milk. The term fat is a short form for fatty acids, an essential nutrient to the body and not, unlike the name may suggest, something that will be stored as fat in the body. Fatty acids are not stored in the human body as fat. The human body stores the poisons, such as fructose, and the fuel in the form of glucose that it breaks down from carbohydrates from plants as fat.

Even the teeth rot and decay that plenty of people suffer from is a consequence of the consumption of plant based foods. The saliva of carnivores, such as humans, is designed to break down carbohydrates for a secondary food source to gain energy and keep going because in the wild a carnivore will not have access to enough meat every day. But it's not meant to be a primary food source. The amylase in the saliva will break down the carbs in the mouth, you can test it with any piece of bread or other baked good, it will dissolve in your mouth over time just from contact with your saliva, you don't even have to bite into it. But biting into one's food is a habit of carnivores. As you bite into the carbs, the amylase that tries to break down the plant matter will damage your teeth if it stands in the way as collateral in the process. You can observe the same in all other carnivores, like dogs, cats or even chickens. They will eat animal derived foods any day, they will not like to eat heavy carb food but if there is nothing else around they will still eat it and survive on it as supplement for the amino acids that otherwise get used up if no more carbs are stored in the body in the form of fat.

If you want to lose weight that badly, you should try yourself at a ketogenic diet. A ketogenic diet simulates to the body that it is starving by leaving out all the carbohydrates. The body always has two options for its energy source, amino acids and glucose. And if all the glucose from the carbs is used up, it will run on power mode with amino acids because amino acids are a much more powerful fuel for the body, but it is also a more valuable fuel because meat and fat does not grow on trees and unlike glucose, it is not just an energy source but an essential nutrient. It is the healthiest way to lose weight.

Great Idea.

Do you know a better way to lose weight? THANKS.

Mixing flavors like honey, mustard, and blue cheese can create a delightful combination of sweet, tangy, and creamy elements. Enjoy your salad!