Cut tenderloin in half and set the thinner end to the side. Cut the thicker end in half lengthwise so you have 3 pieces that are similar in size.

Make the marinade: Combine onion, thyme, vinegar, garlic, habanero peppers, ginger, soy sauce, vegetable oil, brown sugar, allspice, black pepper, cayenne pepper, nutmeg, and cinnamon in a blender. Puree until smooth, stopping to scrape down the sides as needed.

Pour marinade into a resealable plastic bag. Add pork tenderloin pieces, coat with the marinade, squeeze out excess air, and seal the bag. Marinate in the refrigerator for 4 to 6 hours.

When ready to cook, preheat an outdoor grill for high heat and lightly oil the grate.

Grill pork on the preheated grill, moving as necessary to avoid overcooking the thin parts of the meat, until dark grill marks appear and the pork lifts easily from the grill, 6 to 7 minutes per side. An instant-read thermometer inserted into the center should read 145 degrees F (63 degrees C).