When ready to cook, start the Traeger on Smoke with the lid open until a fire is established (4-5 minutes). Turn temperature to 225 degrees F and preheat, lid closed, for 10 to 15 minutes.
Puree 1/2 cup brown sugar, paprika, cumin, fennel, cayenne, garlic, zest of 1 grapefruit, all grapefruit segments, and salt in food processor until very smooth. Reserve 1/4 cup for grapefruit sauce, then transfer mixture to large bowl.
Add pork tenderloin to bowl and completly cover all sides of meat. Wrap with plastic wrap and leave for 15 minutes at room temperature.
For the grapefruit sauce, combine 1/4 cup reserved marinade with 1/2 cup chicken stock in a BBQ safe pot or bowl. Place on Traeger grill.
Place tenderloin on Traeger for approximately 3 hours, or until the pork reaches an internal temperature of 145 degrees F.
Meanwhile, slice ½” disk shipped slices of polenta. Spray tops with olive oil cooking spray, spread dijon mustard on each disk, and divide remaining 1/2 cup of brown sugar on each disk.
At the 2 hour mark, place the polenta disks on the grill evenly spaced for approximately 1 hour, or until disks have crispy edges.
Vinaigrette: Thoroughly mix together grapefruit juice, olive oil and honey. Set aside.
Once pork tenderloin has reached 145 degrees F, remove from grill and let rest for 10 minutes before slicing into 1/2 inch medallions
To serve, place pork medallions on top of a polenta slices. Drizzle greens with vinaigrette. Enjoy!