Mix together butter, parsley, lemon juice and 1/4 teaspoon garlic powder. Place butter mixture in plastic wrap and roll into a log shape. Chill until firm. Combine black pepper, white pepper, red pepper flakes, coriander, sugar, salt and garlic powder.
Rub spice mix into both sides of steaks. Shake off excess. Place steaks on a hot grill and cook for 2 minutes. Turn and cook for 2 additional minutes.