Preheat the oven to 350 degrees Fahrenheit. Grease a 9 by 13-inch pan with butter (don’t be tempted to use cooking spray; it doesn’t work nearly as well).
In a large skillet, warm the olive oil over medium heat until shimmering. Add the bell pepper and green onion and cook until the pepper is tender and cooked through, about 8 to 10 minutes.
Add the spinach to the skillet and cook, while stirring, until wilted, about 2 minutes. Set the pan aside to cool for a bit while we prepare the egg mixture.
Crack the eggs into a medium mixing bowl. Add your dairy of choice, several dashes of hot sauce, plus the salt and pepper. Whisk just until the egg yolks and whites are blended.
Stir in half of the cheese (we’re reserving the other half for topping the frittata before baking). Transfer the lightly cooled veggies into the bowl, and stir to combine.
Pour the mixture into the prepared pan. Evenly disperse the remaining cheese on top.
Bake for 15 to 20 minutes (keep an eye on it), until the eggs are puffed and appear cooked, and the center of the frittata just barely jiggles when you give it a gentle shimmy. For good measure, insert a fork about ¼-inch into the center of the eggs and make sure the fork comes out clean.
Place the frittata on a cooling rack until you’re ready to serve. Slice with a sharp knife, and serve. Leftovers will keep well for about four days in the refrigerator. Enjoy leftovers chilled, at room temperature, or gently reheat in the microwave or oven.
