Preheat the oven to 425 degrees F. Line a baking sheet with foil.
Put the turkey in a bowl and add the celery, garlic, onion, salt and pepper. Mix well and scoop into golf ball-size meatballs. Place them onto the prepared baking sheet as you go. Bake until cooked through and browned, 15 to 17 minutes.
Meanwhile make the sauce. Add the mango, barbecue sauce, agave, soy sauce and habanero peppers to a saucepan with 1/2 cup of water and stir. Bring to a simmer and cook for 10 minutes to thicken slightly and enhance the heat of the peppers. Puree with an immersion blender or use a food processor.
Toss the meatballs with the sauce until well coated. Place on a serving platter and garnish with the sliced green onions.