Preheat oven to 350°F (175°C).

Grate zucchini.

Finely chop onion.

Slice mushrooms.

Sauté mushrooms and onion in a pan until softened.

In a large bowl, combine grated zucchini, sautéed mushrooms and onion, flour, garlic salt, and fresh basil or rosemary.

In a separate bowl, lightly beat eggs.

Add sour cream or yogurt to the beaten eggs and mix well.

Pour the egg and sour cream mixture into the zucchini mixture.

Add grated Cheddar cheese and Parmesan cheese to the zucchini mixture.

Mix all ingredients until well combined.

Pour the mixture into a greased baking dish.

In a small bowl, mix bread crumbs with extra Parmesan cheese.

Sprinkle the bread crumb mixture evenly over the top of the frittata.

Bake in the preheated oven for 40 to 45 minutes, or until the frittata is set and golden brown.

Let cool slightly before slicing and serving.