Make the marinade: in a small bowl, whisk together 1/4 cup olive oil, 1/3 cup honey, 1/3 cup orange juice, 2 tbsp brown sugar, 3 tbsp Dijon mustard, 3 tbsp yellow mustard, 1 tbsp Cajun seasoning, 1/2 tsp salt, 1/2 tsp garlic powder, and 1/4 tsp black pepper until smooth.
Reserve about 1/2 cup of the prepared marinade in a separate container for the sauce, then place the chicken and the remaining marinade in a large freezer bag; seal and marinate at least 1 hour or up to overnight in the refrigerator.
Before cooking, if refrigerated, let the chicken sit at room temperature 15–30 minutes while you prepare the sauce.
Prepare the creamy sauce: add the reserved marinade, 2 tbsp loosely packed cilantro, 3 tbsp sour cream, and 2 tbsp mayonnaise to a blender and process until smooth; set aside.
Stovetop option: heat a large nonstick skillet over medium-high until very hot. Remove chicken from the bag, pat dry, and add to the skillet. Cook undisturbed 3–5 minutes until browned, flip, cover, reduce heat to medium, and cook 5–7 minutes more until cooked through (165°F).
Grill option: preheat and oil the grill to medium (about 375–450°F). Remove chicken from the bag, pat dry, and grill 5–7 minutes per side until cooked through (165°F).
When cooked, remove the chicken, brush or spoon the creamy Cajun honey mustard sauce over it, and let rest 5 minutes before slicing.
Serve sliced chicken topped with chopped mangoes; optionally adjust flavor with a sprinkle of cayenne for heat or extra brown sugar for sweetness.