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 :)
Rice, lentils, cheap vegetables (vary a bit) and dry broth.
I ate this for every meal for a couple of months when I was really poor. I took vitamins and fish oil as well.
Got some meat and dairy when eating with friends and family.