Heat the olive oil in a 10-inch nonstick cast-iron skillet over a medium high flame. When it is hot, add the zucchini and yellow squash. Season with salt and pepper. Saute until lightly caramelized, about 6 minutes.
When the zucchini and yellow squash are browned and softened, add the garlic and cook for 1 more minute. Add the tomatoes and toss to warm through. Add the eggs and begin to stir with a silicone or rubber spatula. When the eggs begin to show signs of setting, season with salt and pepper and place the skillet in the oven.
Cook the frittata until the center sets, about 20 minutes. Remove the frittata from the pan by turning it out or sliding it out with the help of a spatula underneath one side.
Garnish the frittata with the feta cheese, dill and parsley.
The low oven temperature allows the eggs to cook slowly and remain moist, as opposed to a high temperature oven which would cause the frittata to "souffle."