Trim halved turkey breast slices of all fat and skin. Butterfly meat by using a sharp knife, starting in center of one long side and cutting in half to within 1/2" of second long side; open meat like a book (using partially frozen turkey makes this process easier). Set meat flat on a platter. Mix together yogurt, chili, cumin, pepper, nutmeg, and garlic powder in a small bowl. Rub mixture over turkey, cover, and chill overnight (or at least 2 hours). Prepare barbecue. Grill meat 4 inches from heat source until cooked through, about 4-6 minutes per side. Let stand for 5 minutes, then cut diagonally into slices. Serve with a rice salad. Makes about 6 servings.