Preheat oven to 400°F.
Heat oil over medium heat in a large oven-safe nonstick skillet.
Add the onion, zucchini, and tomatoes and sauté until they begin to soften. About 5 minutes.
Add in the baby spinach until it begins to wilt. Remove from heat.
In a small mixing bowl, whisk together the eggs, milk, salt, and pepper.
Pour the egg mixture into the skillet over the cooked vegetables
Sprinkle with cheese and bake in the preheated oven for 10-15 minutes or until the eggs are set and the cheese is bubbly.
Carefully remove pan from the oven and allow to cool for at least 5 minutes before slicing.
Slice and top with fresh herbs.