Crustless Spinach Quiche

INGREDIENTS

• 1 tablespoon vegetable oil
• 1 onion, chopped
• 1 (10 ounce) package frozen chopped spinach, thawed and drained
• 5 eggs, beaten
• 3 cups shredded Muenster cheese
• 1/4 teaspoon salt
• 1/8 teaspoon ground black pepper