Just the usual stuff…
.1. It should be less than your Total Daily Energy Expenditure of calories if you’re trying to lose weight.
.2. It should be nutritionally balanced, ideally cooked from ingredients yourself instead of highly-processed prepared foods.
.3. It should be satisfying and something you enjoy.
I’m not a vegetarian, but I do volume eating. I’m doing two meals a day. I had a few unsuccessful attempts at switching to OMAD. It’s mental and physical change from volume eating to calorie dense foods that I blame for failing. I definitely don’t know how I would do it if I were a vegetarian. I think you should sit down and plan most carefully. One meal after another with calories and macros. Good ratio protein, fats, and carbs in your calorie window. I’m not saying that is impossible for you but I would have problems with that. There is only so much tofu you can eat during a one meal. Love beans and legumes and nuts, but still. Try it on a paper or an app first. Good luck!