Preheat oven to 375 degrees.
Chop and slice all vegetables. Set aside.
Heat olive oil in a cast iron skillet. Add onion, garlic, mushrooms, zucchini, and summer squash to the skillet. Saute until onions are translucent about 4-5minutes total.
Meanwhile, crack all eggs into a medium bowl, add milk, salt and pepper, and whisk until fully combined.
Once the vegetables are cooked, pour the egg mixture into the cast iron skillet. Place tomato slices on top and sprinkle with desired cheese.
Transfer to preheated oven and bake for 25minutes or until the top and edges have started to brown.
Remove from oven and cool for 5 minutes. Drizzle with pesto.
Garnish with freshly cut basil and slice into triangles for serving.