Chicken & Spinach Pasta

Ingredients

• 1-1/2 cups uncooked medium pasta shells
• 1 medium onion, chopped
• 1 large portobello mushroom, chopped
• 2 garlic cloves, minced
• 1 teaspoon olive oil
• 1 tablespoon all-purpose flour
• 1 cup fat-free milk
• 1/2 cup reduced-sodium chicken broth
• 2-1/2 cups cubed cooked chicken breast
• 1 package (10 ounces) frozen chopped spinach, thawed and squeezed dry
• 6 tablespoons shredded Parmesan cheese, divided
• 1 teaspoon lemon juice
• 1/4 teaspoon pepper
• 1/4 teaspoon crushed red pepper flakes