Heres a sample of Sentinel's list of lazy healthy cheap foods. Buy my book titled "how to survive uni on something other than ramen and pizza and still have plenty of booze money"
Get some rolled oats and yogurt (the liquid one that you drink, not the thick one that you eat with a spoon) and shit like chia/flax/black seeds. Grab a big mug, fill it 1/3 with oats, 1 table spoon of each of the seeds, 1/3 yogurt, mix it and let it soak for 3-4 mins. There you go, ridiculously cheap healthy breakfast that takes 3 minutes to make. Almonds work too, just dont get roasted ones since they've got too much salt.
Or soft boil 2 eggs and eat them with toasted whole wheat rye bread. 5-10 mins of prep time. Personally I use bread from sprouted wheat and rye, it's more expensive than regular bread but it's more filling and 5 slices have almost 1/2 of your ideal daily fiber intake.
Bake chicken breast with potatoes or rice or just eat it with salad. 10 min prep time (season it and slice the potatoes while preheating the oven to about 180-200 Celsius) and 30 min cook time where you can just sit around and do something else.
Fish is god tier. I hate canned tuna and salmon is expensive here (thirdie country lul) so I just use frozen hake (very tasty without spices, very lean protein). Get like 200-400 grams or however much you wanna eat, clean it if needed, defrost if needed, bake in a 180C preheated oven for 30 ish mins, add some lemon and whatever side dish you want
If you don't want to cook them yourself, canned beans and peas are god tier sides, just make sure they don't have any additives.
You can cook rice and buckwheat on a stove in single portions and it takes about 20 mins. Get a small pot, put a bit of butter in it, let it melt on medium heat with some onions (or use oil and heat it up). Add rice and stir fry it for like a minute, season, add water (2:1 water to rice ratio works fine) and keep stirring on medium heat till the water gets absorbed (15-20 mins, just listen to a podcast or whatever while you do it). You can also replace some of the rice with buckwheat to make it healthier or add some sliced mushrooms at the start for extra flavor.
Protein shakes or fruit/veggie smoothies also take 2 mins to make and are extremely cheap unless you use exotic shit. One that I'm fond of is 1 banana 1 carrot 1tbsp each of black/chia/flax seeds and 75 grams of dry roasted soy beans. That's 30-40 grams of protein, tons of vitamins, complex carbs and fiber for a ridiculously low price and short prep time. And in case you're actually looking at the soyboy memes kids these days love, don't worry, you'd need to be eating 18+ servings of soy per day every day to even begin to be at risk from the estrogen agonists in it.
Apart from the usual healthy greenies that you'd want to use in smoothies, remember that aronia/blueberries/cranberries are god tier ingredients. A banana is almost necessary to give the smoothie actual texture so you don't feel like you're drinking cold vegetable stock.
Edit: oh ya, when baking, if you don't want to spend ages getting bits of burnt food off the pan, grab a roll of cooking paper and use it to line the pan (aluminum foil works too but it also taints your food with traces of aluminum so don't overuse it). Of you can't get it to match the pans shape, crumple it up into a ball and then uncrumple it (life tip sponsored by Martha Stewart)