Place the chicken between two sheets of parchment paper and pound to an even thickness. Place in a zip close bag and add the mango margarita mix, olive oil, garlic powder and lime juice. Marinate the chicken for 2 to 3 hours (the longer, the more intense the flavor).
Heat the grill over medium high heat and brush the grates with olive oil. Season chicken with salt and pepper then grill chicken for 3 to 4 minutes per side. Remove the chicken to a plate and cover loosely with foil.
Meanwhile prepare the mango salsa by combining all the ingredients in a bowl and stirring to combine. Serve the chicken with the salsa on top.