In a food processor, combine the stripped leaves from about 5 rosemary stems, the olive oil, 3 cloves of garlic, 1 teaspoon sea salt and 1 teaspoon pepper. Pulse to roughly chop.
Coat the pork tenderloin with the herb-garlic mixture, wrap in saran wrap, and allow to sit in the refrigerator in a shallow dish for one hour up to overnight.
Shortly before you are ready to grill, preheat the grill to 500°F and coat the grates with high-heat oil.
Slice the remaining garlic bulb in half widthwise and brush with olive oil.
When the grill is ready, place the tenderloin on the grates along with the garlic halves, cut side down.
Insert the Spark probe horizontally into the thickest part of the meat and set the probe temp to 145°F on your app (you can insert the second one the same way into the other side of the meat). Close the lid and cook, flipping once halfway through cook time, for 12-18 minutes total. Check the garlic around 10 minutes and remove when the cloves are soft.
Remove the tenderloin from the grill and let stand on a board, tented with aluminum foil, for about 10 minutes.
Slice the tenderloin and serve with some of the grilled garlic and the remaining fresh rosemary.