In a large skillet, saute the red pepper and onion in oil until tender. In a large bowl, beat eggs and milk. Stir in the chicken if desired, 1/2 cup spinach, mozzarella and Parmesan cheeses, salt and pepper (save remaining spinach for another use). Add to the skillet. Cover and cook over medium heat until a knife inserted in the center comes out clean, 7-10 minutes. Cut into wedges.