Cook bacon in a Dutch oven over medium heat until crisp. Remove bacon from pan, reserving 1 tablespoon drippings in pan. Crumble bacon; set aside.
Add garlic to drippings in pan; cook over medium heat 1 minute. Add wine and crushed red pepper. Add mussels to pan; cover and cook 6 minutes or until shells open. Remove from heat; discard any unopened shells. Place mussels in a bowl. Add sliced red onion and spinach to wine mixture in pan; cook 1 minute or until spinach wilts. Divide spinach mixture among 4 plates; sprinkle evenly with bacon. Arrange mussels over the spinach mixture; drizzle evenly with any remaining wine mixture.