Coat a large ovenproof skillet with cooking spray, and melt 1 teaspoon butter over medium heat. Add leek, and sauté 4 minutes or until softened. Set aside.
Whisk eggs, egg whites, milk, Parmesan, oregano, salt, and pepper in a large bowl. Stir in linguine, collards, and reserved leek.
Melt remaining 1 teaspoon butter in skillet over low heat. Pour egg mixture into skillet; cover and cook 10 minutes or until the top is set. Meanwhile, heat broiler.
Sprinkle frittata with mozzarella, and broil 3 minutes or until golden brown. Cut into wedges.