Sprinkle Cajun seasoning, kosher salt, and pepper on both sides of the Turkey breast tenderloins.
Preheat the Traeger/ pellet grill to 400 degrees. Place the turkey on the grill grates for 20 to 25 minutes, flipping halfway through. Remove once they have reached an internal temperature of 165 degrees.
While the Turkey rests, set a skillet over high heat and add the butter, heavy cream, garlic, Dijon mustard, and some Cajun seasoning. Once it's bubbling reduce the heat to medium low and simmer for 5 minutes, stirring a few times.
Slice the Turkey and serve with the Cajun cream sauce over top.