Preheat the oven to 375°F (190°C) and grease a 9×13-inch baking dish.
Heat the olive oil in a skillet. Cook the zucchini and bell pepper for 4 minutes, then add the spinach and let it wilt.
Whisk the eggs, cottage cheese, garlic powder, basil, salt, and black pepper until evenly combined.
Stir in the cooked vegetables, green onions, and mozzarella. Pour the mixture into the prepared dish.
Bake for 35 to 40 minutes, until the center is firm and the edges are lightly golden.
Let the casserole rest for 10 minutes before cutting. Cool freezer portions completely to prevent ice crystals.