Toast cumin seeds and peppercorns in a small dry skillet over medium heat, shaking skillet often, 3 minutes or until spices are fragrant. Transfer to a plate to cool, and crush spices with a mortar and pestle. (You can also transfer spices to a heavy-duty zip-top plastic bag, seal bag, and crush with a meat mallet or rolling pin.) Set aside 1/2 teaspoon spice mixture for salsa.
Sprinkle pork with remaining spice mixture, mint, and garlic, pressing to adhere. Cover and chill up to 8 hours.
Sprinkle pork with salt, and grill, covered with grill lid, over medium-high heat (350° to 400°), turning every 5 minutes, 18 to 20 minutes or until thermometer registers 155° and tenderloin is slightly pink in center.
Place pork on a cutting board; loosely cover with foil, and let stand 10 minutes. Cut into slices, and serve with Green Apple-Cucumber Salsa.