Mushroom, Pepper and Feta Breakfast Casserole

Ingredients:
8 oz. sliced mushrooms
1 large green bell pepper, coarsely chopped into pieces about 3/4 inch square
1-2 tsp.olive oil, to saute mushrooms and green peppers
3 green onions, white and green parts, sliced
1 cup crumbled feta (or more, to taste)
18 eggs
ground black pepper to taste