Marinate the turkey tenderloin by placing it in a bag or dish and pouring the garlic butter mixture over it. Seal tightly and refrigerate for at least 30 minutes.
Preheat oven to 375°F (190°C). Place the marinated turkey on a lined baking sheet and roast for 25-30 minutes until cooked through (internal temperature of 165°F/75°C).
Let the turkey rest for 5-10 minutes before slicing to retain moisture.