I think eating monomeals is most popular among raw-food vegans. However, eating monomeals is a great way to determine if you are allergic to foods.

I don't believe there is hard evidence to say that a monomeal is healthier than a non-monomeal.

I think that only applies to anything eaten with grains or legumes, there is a name for that diet but I can't think of it right now (in German it's "Trennkost"). One should never eat raw fruit with aforementioned cooked carbs, with cooked protein (meat) fruit is O.K. I don't remember the exact reasoning behind it either. In paleo terms I could imagine maybe combining starchy vegetables with raw fruit could cause digestive issues, but don't ask me why and how, it's just a general thing I remember. On the other hand protein, fat, and carbs from veggies go very well in one meal and support eachother's digestion and chemical reaction in the body. I'm sorry I can't give you any data, it's just things I remember reading here and there and acting by and can confirm that for example a starchy vegetable eaten with fat digests much better and I believe to have read somewhere also raises blood sugar slower and not as high.