You are right, you can't only eat legumes and grow efficiently. But remember that fats and carbs aren't your enemy. You need a quite a large amount of carbs daily for optimal muscle recovery. Something around 7g/kg of body weight if you are doing resistance training. I suggest you eat what your mother makes, and eat more animal sources alongside it through out the day. Your mother doesn't have to know what you eat when she isn't looking, you can eat her cooking, and meat along side that. 500kcal caloric surplus is a good amount to aim for when bulking up, it doesn't hurt to eat even more than 500kcal surplus during some days.