I've started using a supplement called humapro which gives you the amino acids without the calories. So basically an equivalent to 25g protein is less than one calorie.
Other than that, I focus on eating whole foods as every whole food has some protein. Leafy greens tend to have the highest protein content but they weigh so little, it takes a lot
. Green smoothies are a good way to get a lot of leafy greens in one meal.
And how much protein are you eating? I aim for about 80g or so per day.