Look into fresh produce that you can eat raw. IMHO there's no nicer snack than a crisp crunchy carrot. They're cheap, and pretty much always available. Carry a mini peeler with you and you can just grab one from a store, peel it over a rubbish bin, and scoff it. :)

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

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

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

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!

Whole grain pasta.

Fried grasshoppers

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.

Homemade Popcorn!

Purple asparagus! You can grow it and it grows in incredible quantity quite quickly. Then you can toss it in the air fryer each day for ten minutes with some seasonings and it's phenomenal.

potatoes!

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

You should shop at a grocery outlet, that's how you get all three achieved. there's so much cheap overstocked healthy food, because originally was too expensive and people didn't want to pay that much, so I benefit. Best grocery store there's ever been, prove me wrong!