unless you're doing a very low calorie diet, you can just eat more of the beans. plugging it into cronometer, it would take 1050 calories of pinto beans to meet my protein needs (woman in my late 20s). this is mostly because of cystine, which is less present in plant sources than animal sources, otherwise it would be even lower.

what this means is that in practice you should be fine as long as you're limiting distilled oils and sugar and generally getting enough to eat. even if you don't eat this much beans, other vegetables have protein too so you just need to meet your caloric needs.

the exception is if you are eating a very low calorie diet, say around 1200 calories, then you might need to worry about it more since having beans be 88% of your diet isn't good. since oats have a higher amount of cystine than buckwheat, they are probably a better choice in this scenario.

if a person had 2 cups pintos + 1 cups oats (800 calories) i would guess it would be close to impossible to not meet their protein needs during your remaining 400 calories. 1.5 tablespoon peanut butter (150 calories) would meet the rest of a sedentary woman's protein needs, which is typically the only type of person who should be eating this little.