Add peanut butter or coconut oil to your smoothies. Yum! Or make your favorite soup and puree it -- beans puree nicely in soups, and if you're not sure you want a lot you can always add part of a can of refried beans... already mashed! Again, if you're not getting enough calories, add eggs or fats to your soups.
Soft-cooked eggs might be easy to eat, too.
Cottage cheese is pretty soft. Hard cooked eggs mashed up with cottage cheese and flavored with mustard makes a kind of deviled-egg-tasting dish that would be fairly soft.
Fruits can be stewed or cooked into sauces and added to yogurt or pudding.
Some veggies can be stewed, like one of my faves -- tomatoes and spinach (it's how I learned to like spinach; now I can eat it alone but I still love it stewed with tomatoes). Cauliflower, parsnips, squash, carrots, and potatoes all can be mashed and are soft.
Google recipes for "congee", which is an Asian rice porridge. Or oatmeal made with milk (or cream for more calories) and fruit is a good soft porridge.
Here are some links
for soft food diets, which will give you more info on what you can eat and what you should avoid.
Good luck on the dental surgery! Recover quickly and fully!