Asparagus-Mushroom Frittata

Preheat oven to 350°. In a large bowl, whisk eggs, ricotta cheese, lemon juice, salt and pepper. In a 10-in. ovenproof skillet, heat oil over medium heat. Add asparagus, onion, red pepper and mushrooms; cook and stir 6-8 minutes or until onion and pepper are tender., Remove from heat; remove asparagus from skillet. Reserve eight spears; cut remaining asparagus into 2-in. pieces. Return cut asparagus to skillet; stir in egg mixture. Arrange reserved asparagus spears over eggs to resemble spokes of a wheel., Bake, uncovered, 20-25 minutes or until eggs are completely set. Let stand 5 minutes. Cut into wedges.