Preheat your oven to 375°F. In a large bowl, whisk together eggs, milk, salt, and pepper until well combined. Set aside.
Heat olive oil in a 10-inch oven-safe skillet over medium heat. Add onion and bell pepper, cooking for about 5 minutes until softened.
Add spinach and cherry tomatoes to the skillet, cooking for another 2-3 minutes until spinach is wilted.
Pour the egg mixture evenly over the vegetables in the skillet. Sprinkle cheese on top and gently stir to distribute ingredients.
Cook on the stovetop for 3-4 minutes without stirring, until edges begin to set.
Transfer the skillet to the oven and bake for 15-18 minutes, until the center is set and the top is lightly golden. Let cool for 5 minutes before slicing into wedges.