- Preheat oven to 350ºF and lightly grease a 10-inch pie pan with butter or oil. Combine panko, flour, melted butter and egg in a mixing bowl. Stir until well moistened.
- Press panko mixture into prepared pan. Bake for 10 minutes. Remove from oven to cool while preparing filling.
- Heat oil in a large skillet over medium heat and add mushrooms and leeks. Sauté for 5 minutes. Add spinach and continue to cook for 2 minutes, stirring regularly. Set aside to cool for 5 minutes.
- Whisk eggs, Italian seasoning, and salt in a large mixing bowl. Stir in vegetables and cheddar cheese.
- Pour into crust and bake for 25-30 minutes. Cool for 5 minutes before slicing.