I'm more in the camp of eat more vegetables. My wife and I have been ovo-lacto vegetarians for over 50 years. We do get hungry and then eat, which fixes that hunger problem. I always have my HRM active and watch my HR. Occasionally on long rides, I'll see my HR go lower then is should be for my RPE. That's always a sign that need to eat even if I don't feel hungry. Sometimes my HR will be high for the RPE, which means I'm getting dehydrated. More information is better than less.
I don't think it matters a heckuva lot what one eats the night before as long as dinner contains a moderate amount of carbs. The general rule is 1/2 the plate veggies, 1/4 carbs, 1/4 protein. The protein can be dairy, fish, or even (shudder) meat. Current rec is 6 oz. of meat per week. Fish and seafood doesn't count as meat in this rec.
https://www.mayoclinic.org/healthy-l...n/art-20048095
We eat a good bit of nuts, legumes, and dairy which includes whey protein.
The only times I've ever had stomach problems was from eating too much before or during a long hard climb. One can bonk from doing that because if stomach osmolality is too high, food can't move across the stomach wall and one runs out of glycogen. It's known as "sloshy stomach."