Season the pork with the cumin, ½ teaspoon salt, and ¼ teaspoon pepper.
Heat 1 tablespoon of the oil in a large skillet over medium-high heat. In batches, cook the pork until browned, 1 to 2 minutes per side. Transfer to a plate.
Meanwhile, heat the remaining tablespoon of oil in a second skillet over medium-high heat.
Add the onion and bell peppers and cook, stirring occasionally, until tender, 6 to 8 minutes.
Serve the tortillas with the pork, vegetables, avocado, cilantro, and sour cream.