For the pork: Combine the cilantro, lime juice, oil, chile powder, garlic and onions in a large dish. Add the pork slices and turn to coat. Preheat a grill on medium-high heat.
For the red slaw: Combine the cabbage, cilantro, oil, vinegar, chile powder, bell peppers, red onions and 1/4 teaspoon each salt and pepper in a large bowl. Toss to mix and set aside.
Remove the pork from the marinade and discard the remaining marinade. Sprinkle the pork on both sides with 1/4 teaspoon each salt and pepper. Grill, turning once, until browned and still a little rosy inside, about 10 minutes. Transfer to a large plate.
Grill the tortillas, turning once, until grill marks appear and the tortillas are softened, about 1 minute. Transfer to individual plates. Divide the pork and a little slaw among the tortillas. Top each tortilla with a teaspoon of sour cream and serve with lime wedges.