Preheat oven to 190°C.
Whisk eggs with 2 tablespoons water and set aside.
In a large sauté pan over medium high heat, add olive oil. Add mushrooms and sauté until tender and all liquid has evaporated, about 5 minutes.
Add garlic and parsley and cook 1 minute more. Stir in parsley and season to taste.
Pour eggs over mushrooms, stir just to combine, then sprinkle with grated cheese.
Place pan in oven and bake, uncovered, until eggs have set and cheese has melted, about 15 minutes. Turn fritatta out onto a plate and cut into wedges to serve.