Preheat oven to 450 degrees. In a small saucepan over medium heat, combine the butter, mustard, lemon juice, garlic, and parsley. When the butter melts completely, remove from heat. Arrange shrimp in a shallow baking dish. Pour the butter mixture over the shrimp. Bake in preheated oven for 12-15 minutes or until the shrimp are pink and opaque.