This is my go to base for a quiche. I always do crustless. You can add really anything to this. We love sauteed veggies with onion and garlic with ham or tomatoes and bacon. If you cook the veggies, let them cool before adding to quiche mix because of the eggs. Spinach and ham is classic with added swiss. This is really great for when you have random veggies and leftover meat or deli meat in the fridge!
Scale back the mozzarella to a 1/2 cup and put1/2 cup any other kind of cheese in, I use cheddar, swiss, provolone, parmesean frequently. I have also used cottage cheese with the ricotta.