Combine oil, rosemary, maple syrup, mustard, and soy sauce. Pour over tenderloins and spread to coat evenly.
Marinate tenderloins in refrigerator for at least two hours, if possible. If you don't have time to marinate that long, aim for 15-30 minutes if you can. It's still gonna taste great.
Cook on the grill at medium heat, approximately 8 - 10 minutes per side. Be sure to cook until internal temp hits 165 degrees Fahrenheit.
Let the cooked turkey rest for a few minutes before slicing (and maybe you could take a few minutes of well-deserved rest, too?). This allows the juices to redistribute throughout the turkey so that it can retain the juices rather than flow out onto your cutting board.