This "recipe" is infinitely variable, and has no rules. Experiment!
--Approximately 3 cups of cooked rice or other grain, or potatoes
--1 large onion and
--Several cloves of garlic, optional
--1 large bunch broccoli, or kale, or greens of your choice, chopped
--A couple smaller veggies (turnips, carrots, etc.), chopped small, optional
--salt and pepper
--herbs and spices (~2 tsp. basil and ~.5 tsp. oregano is nice)
--sprinkling of red pepper flakes
--1 dozen eggs
--0-2 cups milk (the more you use, the more tender the frittata will be. No milk will yield a slightly drier, firmer frittata
--Some chopped parsley
--4-8 oz. grated cheese
--Thinly sliced veggies for the top (tomato, peppers, etc.)
Butter a 9x13 casserole, or the equivalent, and preheat the oven to 350f. Enamel-lined pans are easier to clean.
Put the potatoes/rice in the bottom of the pan (or, if you're not concerned with aesthetics, and to make cooking quicker, stir them into the veggies at the last minute, which will heat the rice/potatoes and speed baking). Spread 2/3 of the grated cheese over this.
For more even cooking, heat the milk in the microwave until warm.
Saute the onion until it starts to brown. Add garlic and broccoli/greens/veggies, and cook until partway done (they will cook more in the oven). Season with spices and salt and pepper until tasty.
Beat eggs with milk, and chopped parsley if using.
Spread vegetable mixture over the rice/potatoes/cheese. Put the remaining cheese on top, pour milk/egg mixture evenly over the top, and put thinly sliced veggies decoratively over the top of this.
Bake for about an hour, until the center is not liquidy and the inside temp. registers 160 or more on an instant-read thermometer.