Preheat the oven to 450 degrees F. Mix the lime zest and cumin in a small bowl. Rub the pork all over with 1 tablespoon olive oil, then coat with the cumin mixture. Season generously with salt and pepper. Heat the remaining 2 tablespoons olive oil in a large ovenproof skillet over medium-high heat. Add the pork and cook, turning, until browned on all sides, about 5 minutes. Transfer the skillet to the oven and roast until a thermometer inserted into the center of the pork registers 145 degrees F, 15 to 20 minutes. Remove the pork to a cutting board and let rest.
Meanwhile, chop the tomato, plums, cilantro and jalapeno (remove seeds for less heat). Transfer to a bowl and toss with the lime juice and 3/4 teaspoon salt. Set aside, tossing occasionally, until ready to serve.
Warm the tortillas as the label directs. Thinly slice the pork; divide among the tortillas and top with the avocado, plum salsa, cheese and more cilantro.