Preheat the oven to 400 degrees F.
Heat the butter in a 10-inch oven-safe skillet over medium heat. Add the shallots and garlic with a pinch of salt and pepper. Cook, stirring often, until softened and they begin to brown, about 5 to 6 minutes.
In a large bowl, combine the eggs, mozzarella, half and half, oregano, basil and a big pinch of salt and pepper. Whisk together until combined.
Pour the egg mixture right over the shallots and garlic in the skillet. Let it set for 1 to 2 minutes. Then top the frittata with the tomato slices.
Stick the skillet in the oven and bake the frittata for 10 to 15 minutes, or until it’s set in the center. You want the eggs set - if they aren’t, bake it for another 2 minutes and check again.
In a bowl, toss the arugula with the olive oil, lemon juice and a pinch of salt and pepper.
Sprinkle the frittata with the parmesan cheese and crushed red pepper. Top with the arugula greens. Serve!