Place a large nonstick skillet coated with cooking spray over medium-high heat until hot. Add onion, and cook for 3 minutes. Add turkey; cook until browned, stirring to crumble. Add salsa, cumin, half the garlic, and beans.
Place ricotta in a food processor, and process for 1 minute or until smooth. Add remaining garlic, cream cheese, 1/4 cup Parmesan, and egg white; pulse 2 to 3 times. Add the spinach, and pulse 2 to 3 times.
Spread 3/4 cup turkey mixture in the bottom of a 13 x 9-inch baking dish coated with cooking spray. Arrange 3 noodles over the turkey mixture, and top with 1 cup ricotta mixture, 3/4 cup turkey mixture, and 1/4 cup Mexican cheese. Repeat layers, ending with noodles. Spread remaining turkey mixture over noodles, and sprinkle with 1/4 cup Parmesan. Cover with foil; store in refrigerator up to 24 hours.
Preheat oven to 375°.
Bake, covered, at 375° for 30 minutes. Uncover and sprinkle with 1/4 cup Mexican cheese, and bake, uncovered, for 10 minutes. Let stand for 10 minutes. Garnish with oregano sprigs, if desired.