- Prepare Cajun onions: Thinly slice 1 large sweet onion. In a skillet on medium, heat 1 tbsp olive oil. Add onions and pinch sea salt; cook, stirring occasionally, until onions start to turn golden. Add 1/8 tsp each chile powder, cayenne pepper, paprika, garlic powder and onion powder and cook for 30 minutes more, or until sticky and caramelized. (If needed, keep onions from drying out by adding water, 1 tbsp at a time.) Add balsamic vinegar; mix well and remove from heat.
- Meanwhile, prepare mango salsa: Combine mango, cucumber, red onion, lime juice, cilantro, salt and ground black pepper, to taste.
- Prepare burgers: Combine ground turkey, chives, garlic, Worcestershire sauce, chile powder, salt and pepper, to taste. Form into 8 patties.
- In a separate bowl, combine shredded mozzarella cheese and basil. Divide cheese mixture on top of 4 of the patties then stack remaining 4 patties on top of cheese and use your hands to press patties together on the edges, sealing the cheese inside. Heat a grill to medium and lightly oil grate. Grill burgers for 12 to 14 minutes, turning halfway. Serve on 4 whole-grain buns with caramelized Cajun onions and mango salsa.