Place fillets in a shallow bowl. In a small bowl, combine next 4 ingredients (rosemary through black pepper) along with half of the garlic.
Rub mixture into fish then cover and refrigerate for 30 minutes. Preheat grill to MEDIUM and lightly oil grill grate. Meanwhile, prepare Mango Vinaigrette: In a food processor or blender, combine next 4 ingredients (mango, lime zest, lemon juice and olive oil) along with remaining garlic.
Process until smooth then set aside. In a large bowl, toss together baby spinach, red onion, mushrooms, bell pepper and carrots; set aside. Grill flounder fillets over indirect heat for 3 to 4 minutes per side or until fish flakes easily when tested with a fork.
Watch carefully to prevent burning! Arrange salad on dinner plates and top with a hot fish fillet. Garnish with Mango Vinaigrette or serve on the side. Enjoy!!