Add spinach and fat free croutons to large bowl and set aside.
Blend together vinegar, water, mustard, splenda. Set aside. Spray large pan with cooking spray. Cook turkey bacon until crisp, remove and cut into 1" pieces. Add onion and garlic to pan and saute 1-2 minutes. Add vinegar mixture and simmer 1-2 minutes. Pour over spinach and croutons.