Step 1: Trim any silverskin off the pork tenderloins.
Step 2: Prepare the marinade: Toast the cumin seeds and peppercorns in a comal over a medium heat until fragrant, 1 minute. Transfer to a blender. Roast the tomatoes, onion, and garlic in the comal until darkly browned, 2 minutes per side. Rough chop and transfer to the blender. Add the chipotle with their juices, the orange zest and juice, vinegar, oregano, and salt, and puree until smooth.
Step 3: Pour half the marinade over the bottom of a glass baking dish. Arrange the pork tenderloins on top. Pour the remaining marinade over them and marinate, covered, in the refrigerator for at least 6 hours, preferably overnight, turning the tenderloins a few times, so they marinate evenly.
Step 4: Set up your grill for direct grilling and preheat to high. Brush and oil the grill grate.
Step 5: Remove the pork from the marinade and drain well. Arrange on the grate and grill until cooked to taste, 3 to 4 minutes per side (12 to 16 minutes in all) for medium (150ºF on an instant meat thermometer), basting every few minutes with melted butter or oil. Transfer the tenderloins to a cutting board and let rest for 3 minutes, then slice on the diagonal.
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Steven Raichlen’s Project Smoke is a production of Maryland Public Television, Barbacoa, Inc., and Resolution Pictures. © 2017 Barbacoa, Inc.