Marinate the Pork: In a small bowl, mix the cumin, chili powder, salt, and pepper. Rub the spice mix over the pork tenderloin and let it marinate for 10-15 minutes.
Cook the Pork: Heat 1 tbsp of olive oil in a large skillet over medium-high heat. Add the marinated pork tenderloin and cook for 20-25 minutes, turning occasionally, until the internal temperature reaches 145°F (63°C). Let the pork rest for 5 minutes before slicing it into thin strips.
Prepare the Salad: While the pork is cooking, in a large bowl, combine the mixed greens, cherry tomatoes, red onion, black beans, and avocado.
Make the Dressing: In a small bowl, whisk together the remaining 2 tbsp olive oil, lime juice, salt, and pepper.
Assemble the Salad: Add the sliced pork on top of the salad. Drizzle with the lime dressing and toss gently to combine.
Serve: Garnish with fresh cilantro if desired, and serve immediately. If saving for later use, separate out ingredients to assemble when ready to eat. Refrain from slicing avocado until ready to eat.