Preheat your oven to 350°F (175°C) while preparing the ingredients.
In a large, oven-safe skillet, heat a tablespoon of olive oil over medium heat. Add the diced onion, bell peppers, and cherry tomatoes. Sauté until the onion is translucent and fragrant, about 5-7 minutes.
Add the spinach and cook until it wilts down, which takes about a minute.
In a bowl, whisk together the eggs and milk, seasoning with salt and pepper.
Pour the egg mixture over the sautéed vegetables, ensuring all veggies are submerged. Let it sit on the stovetop for about 2 minutes until the edges just begin to set.
Transfer the skillet to the oven and bake for about 20 minutes, until the center has a slight jiggle and a golden hue develops on top.
Let it cool for a few minutes, slice into wedges, and enjoy warm or at room temperature.
