Preheat oven or grill to 400 degrees.
Combine marinade ingredients in blender and pulse to blend.
Using (4) double-thick 12” squares of foil arrange steak and pepper slices into four portions.
Drizzle ¼ of marinade over each one. (Alternately, add sliced meat and peppers to bowl of marinade sauce and massage in and then divide.) Seal packets, pulling the narrowest sides up together and folding twice, then folding each of the long sides twice to seal the ends. (At this point the packets can be refrigerated for up to 4 hours.) Place packets on grill or in the oven for 25 minutes to cook.
Heat tortillas on the grill (wrap in foil and allow to sit on a cooler side of the grill or quickly cook directly on the grate). Place limes cut side down on the grill until charred and juicy, about 4 minutes. Open steak taco packets tableside and serve with grilled limes, chopped red onion, avocado (or guacamole), and cilantro