Preheat oven to 375°F; lightly oil an 8-by-8-inch baking dish. Use fully cooked rice or pasta and cooked vegetables.
Whisk milk, beaten eggs, salt and pepper in a bowl; fold in cooked grains, vegetables and half the cheese.
Stir in special additions (cooked diced zucchini, chopped drained sun-dried tomatoes) and spoon mixture into the baking dish. Sprinkle remaining cheese on top.
Bake uncovered 30–35 minutes until the center is fully set and an instant-read thermometer registers at least 165°F.
Rest 10 minutes before serving.