Preheat oven to 375 degrees F. Line a 15x10-inch baking pan with foil. Lightly coat with cooking spray; set aside. Stir together the chicken, finely chopped grapes, green onions, bread crumbs, soy sauce, and pepper. Use a cookie scoop to shape into 12 meatballs. Place in prepared baking pan and bake for 20 minutes or until done (165 degrees F).
Meanwhile, stir together the chopped grapes and chili sauce; set aside. Stir together the mayonnaise and curry powder; spread over buns. Top with meatballs and grape relish.