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 :)
Unconventional, but meal replacement shakes could be an option. E.g. Huel or Soylent. They don’t recommend using it exclusively, but there are plenty or anecdotal stories of people doing just that. They (at least Huel the one I’m most familiar with) is designed to be >=100% of all 27 vitamins/minerals with a set macro ratio.
It’s much less active than it used to be, but there is a DIY Soylent community. There’s a pretty good site at:
https://www.completefoods.co/
that ranks the most popular recipes and has a pretty decent app that calculates nutritional value and per meal cost of the various recipes.
edit - looking at it now, I’m not sure if the price calculations per recipe are up-to-date. In particular, I know the cost of protein powder has increased substantially, so your mileage may vary in terms of the listed costs, but the calculator is still very useful for concocting your own recipes and forking/modifying other people’s recipes.