No Stupid Questions

The Instant Pot or equivalent is the best invention for this. Throw in whatever ingredients (beans, veg) were previously too much hassle to cook. Add water, press button, wait for beep, open pot, eat. Well better find some recipes first, but it's almost that simple.

Here's a favorite of mine: 1 cup dry beans, 1/2 cup tomato powder (yes that is a thing), 2 cups water, cook on high pressure for 35 minutes, stir in a can of corn kernels from trader joe. Done and delicious and nourishing, due to the protein combination from the corn and beans mixing. Or use rice instead of corn, except that's more hassle since it's best to make that separately.

Bananas (possibly depend on where you live).

Peanuts and other nuts

My very Italian answer is "pizza bianca" . I guess "healthy" depends, but it's generally OK carbs, it's delicious and with few Euros you can buy quite a lot (enough for a lunch).

Beans! Especially stew with them, you can throw in pretty much anything (veggies, meat, adjust your spice levels...) and once you learn the correct balance it's very tasty and filling.

Fried grasshoppers

Whole grain pasta.

Popcorn is very low calorie per volume, especially the types without a lot of fat.

Carrots. Same as potatoes. Boil em, mash em, stick em in a stew. Someone already mentioned onions, same idea.

I know your edit says you were thinking about dishes, and I think carrots can be their own dish with very little preparation. I like to bake mine on a sheet for half hour or so at 425f, and they are wonderful on their own. Also so low-calorie you can eat a practically infinite amount of them without spoiling a diet!

IMHO, steamed vegetables are right in the middle of the triangle. I've bought a steam cooker and it's a game changer compared to boiling. It's healthier since less nutrients are lost, preserves so much more taste and texture, there's a timer so you can start the steamer and go do something else. Also makes you use less water. I've still got to try steamed fish but I expect it'll taste great.

Chickpeas

My favorite cheap + delicious+ filling meal is eggs and toast.

Peanut butter and banana sandwich is also dirt cheap and delicious.

literally any bagel sandwich, unless the cost of eggs or ham is still rlly high in your area. low effort, immaculate.

Well chicken maybe as it is the most cheap meat. And it is subjective, but something like chicken soup (if cooked at home) can be relativly cheap and really delicious.

Also, just thought about it - fruits and berries also easily break this trinity

Eggs.

Late to the party, but lately I've been addicted to microwavable broccoli florets (just the leafy part, not the stalks) covered in sharp cheddar cheese.

My brain has learned to think it's cheese fries. But it's broccoli.