Preheat the oven to 400 F. Preheat 10” skillet to a medium heat, pure in olive oil and butter, add mushrooms and stir-fry them for 1-2 minutes.
Add chopped onions and sweat another 2-3 minutes, add diced zucchini, toss the mixture well, season with salt and pepper and let simmer at low another 2-3 minutes.
Meanwhile combine eggs, Parmesan and Cheddar, season with a pinch of salt and add them to the skillet, put salami slices and halved tomatoes on the top.
Once the eggs start to set on the side of the pan, put the skillet in the oven and bake for 15 minutes or until frittata sets in the middle.
