Preheat your oven to 375°F (190°C) and lightly grease a 9×13 inch baking dish.

In a skillet over medium heat, add a splash of olive oil. Sauté diced onions and bell peppers until tender (about 5 minutes), then add spinach until wilted.

In a large bowl, whisk together the eggs and milk until combined. Stir in the sautéed vegetables and season with salt and pepper.

Fold in shredded cheddar cheese until evenly distributed.

Pour the mixture into the prepared baking dish and bake for 30-35 minutes until golden brown on top and set in the middle. Allow to cool slightly before slicing.