Preheat oven to 350°F (175°C). Grease a 9x13-inch baking dish with cooking spray or a little olive oil.
In a large skillet, heat olive oil over medium heat. Add onion and bell pepper; sauté until softened, about 5 minutes. Add garlic and spinach; cook until spinach wilts, about 2 minutes. Remove from heat and let cool slightly.
In a blender or food processor, combine cottage cheese and eggs. Blend until smooth. Pour into a large bowl and stir in 3/4 cup of the cheddar cheese, salt, pepper, and red pepper flakes (if using).
Stir the sautéed vegetables into the egg mixture. Pour into the prepared baking dish. Sprinkle the remaining 1/4 cup cheddar on top.
Bake for 30-35 minutes, until the center is set and the top is golden. A knife inserted in the center should come out clean.
Let cool for 5 minutes before slicing into 6 pieces. Serve warm or at room temperature.