Place chicken, onions, garlic, salt, pepper, and flour in a resealable bag. Stir in the lime juice. Allow to sit for a few minutes to marinate.
Spray a non-stick frying pan with olive oil cooking spray and place over medium heat. Pour in the entire contents of the bag and cook until the onion has softened (there is no need to brown). Add additional lime juice to taste. Serve over spinach.
