Set your oven to 375°F (190°C). Lightly coat a baking dish with nonstick spray so the quiche lifts out easily later.
Place a skillet over medium heat and cook the chopped onion for about 5 minutes, stirring now and then, until it turns soft and fragrant.
Crack the eggs into a large mixing bowl, then add the cottage cheese, cooked onion, chopped spinach, garlic powder, salt, pepper, and half of the shredded cheddar. Stir everything together until the mixture looks evenly combined.
Transfer the filling to the prepared baking dish and spread it out evenly. Sprinkle the rest of the cheddar over the top.
Bake for 30 to 35 minutes, or until the center is firm and the top develops a light golden color. Let it rest for a few minutes before cutting into slices.