Heat oven to 425 degrees F. Spray 12 medium muffin cups with no-stick cooking spray or line with paper baking cups.
Stir together muffin mix and 1 cup milk in large bowl just until moistened. Fold in 1/2 cup baking chips and 1/2 cup macadamia nuts. Fill muffin cups about 3/4 full. Sprinkle 1/4 cup macadamia nuts over batter. Bake 13 to 16 minutes or until light golden brown. Cool 2 to 3 minutes in pan. If not using liners, loosen sides of muffins with knife. Remove from pan.
Microwave 1/3 cup baking chips and 1 teaspoon milk in uncovered microwave safe bowl on MEDIUM-HIGH power for 45 seconds. Stir until smooth. If necessary, microwave in 15 second intervals until chocolate is melted. Drizzle over muffins.