Flavor does not matter, presentation does not matter but the food shouldn’t make you sick, and should ideally have enough calories per day for the average person to survive (2000 kcal min).
Edit: I am not in any danger of starving or malnutrition, nor am I insolvent. I’m mainly asking this question out of curiosity on how people would approach a solution :)
If we’re optimizing for cheap and nutritious a lot of the existing answers are probably pretty great, but if there’s no other restrictions on the diet I think we could optimize a little further.
The cheapest way I can imagine to get a nutritional meal is to find someone who eats fully nutritional meals, and then eat them.
But it’s per meal. Consistently finding people to eat and getting away with it sounds like a costly ordeal.