Preheat your oven to 180°C (350°F) and grease a baking dish with oil or butter.
In a large bowl, mix the grated zucchini, chopped celery, sliced mushrooms, and peas.
Add chopped parsley and green onions for fresh flavor.
Stir in the grated cheese and oatmeal.
Crack in the eggs, season with salt and pepper, and mix until fully combined.
Pour the mixture into the prepared baking dish and spread evenly.
Bake for 30–35 minutes, or until the top is golden and the center is set.
Let cool for a few minutes before slicing. Serve warm or at room temperature.