Hi Im a low-income vegan with executive function problems so I thought Id try to list some foods that help me get by when Im having trouble with meals.
Oatmeal can be super helpful. It keeps you full for a while, is easy to make (heat water, add it to oatmeal, bam done) and you can throw some fruits and nuts in there too. I personally hate the texture of oatmeal, so I use bulgur wheat instead which is really similar. Im sure you can find some other alternatives pretty easily if you google it.
Frozen vegetables are super cheap (1-2$ a bag) and you can cook them on the stove in around 5 minutes usually. If you can afford it, fresh vegetables are great because you can just eat them raw.
Kale is also cheap, usually a dollar for a big bunch of it, and you can just snack on it raw. If you dont like the taste, put some olive oil and salt on them and pop them in the oven for a few minutes.
Potatoes- cheap and filling. It does take them a long time to cook, but its a simple process. just poke some holes, rub some vegetable oil on them, and stick them in the oven. takes about an hour, just dont forget to set a timer or something! (you can also microwave them in about 5 minutes. not as tasty and you lose some nutrition, but its so much easier)
Trail mix- not much else to say about this. cheap, tons of nutrients, delicious, and you dont have to prepare anything. (you could also make your own)
When I have extra cash I try to stock up on fresh fruits and veggies, theyre a pretty important part of your diet and you can just keep them nearby to eat raw whenever you dont have the energy to cook.
For times that you do have the energy to cook things, make double the amount so you can have leftovers that you can quickly reheat later. Rice and beans are a good choice because combined, they make a complete protein, plus they are super cheap.
Check to see if your grocery store has a reduced produce section. You can get slightly bruised/old fruit for about half the price. Some places have reduced grocery too, and they mark things down really really cheap just because the box is a little dented etc.