Heat the oven to 375°F / 190°C. Lightly grease a 9 × 13-inch baking dish (or 9 × 9 if you like taller slices) with a light mist of oil or cooking spray.

Crack the eggs into a big bowl and whisk until smooth. Spoon in the cottage cheese and Greek yogurt and whisk again; a few curds are fine.

Stir the bell pepper, scallions, and spinach into the egg mixture. Sprinkle in salt and freshly ground black pepper, then give the mixture one last whisk to distribute everything evenly.

Pour the mixture into the prepared pan and bake on the middle rack for 35-40 minutes or until the center is set and the top becomes golden.

Let the casserole rest for 10 minutes before cutting into squares.