Preheat oven to 400 degrees F.
Prep all your vegetables and set aside. Additionally, in a small bowl, combine shredded mozzarella and parmesan cheese then set aside.
Crack eggs into a medium mixing bowl and whisk until beaten then add yogurt, cheese & oregano.
Place a cast-iron (or other oven-safe) skillet over medium-high heat on the stove top. Once hot add the olive oil (hover your hand over the pan, if you feel the heat, it’s ready for the oil) followed by the broccoli, mushrooms, onion and tomato. Sprinkle with salt & pepper and sauté until veggies are just tender (about 4 minutes).
Pour the egg mixture over the veggies. Allow to sit on the stovetop over medium-high heat for about 4-5 minutes (just until the edges of the dish begin to set).
Once edges begin to set, remove from the stovetop and place in the preheated oven. Bake for 10-15 minutes or until frittata is set (*see note)
Allow to cool then slice and serve!