Remove the fatty membrane from the steak, if applicable (for a how-to on removing the membrane, see this post from Serious Eats for instructions.) If needed, cut the steak so it will fit into the pan you’re going to be using later, but leave it in as long of pieces as possible. Also make sure your pieces are the same size.
Combine all marinade ingredients in a large freezer bag. Add steak to the bag and toss to coat with the marinade. Remove as much air as possible from the bag, and marinate in the fridge for at least an hour.
Prepare the pico de gallo. Cut tomato into large large pieces (probably about 6-8 pieces). Remove the membranes and seeds. Add to a food processor bowl or blender. Cut onion into large chunks, and add to the food processor/blender. Add garlic and salt. Process until the onions and tomatoes are cut to small, uniform sizes. Set aside in the refrigerator.
Prepare the chipotle sour cream by combining all ingredients. Set aside in the refrigerator.
Preheat grill or grill pan to medium-high heat. Once the pan is super hot, coat it with olive oil (or if using a grill, coat grill grates with nonstick high heat spray).
Add steak(s) to the pan and cook undisturbed for 2 minutes. Flip and cook the other side for 2 minutes. Flip again, rotating slightly so the grill marks at an angle. Flip and repeat for the other side. (This cooked them to medium. I did not bring the steaks to room temperature before cooking them. See notes below for food safety information.)
Remove steak from the pan and let it rest for 3 minutes. Cut the steak at an angle against the grain.
Warm tortillas in the microwave for about 10 seconds. Place meat onto tortillas, followed by some Monterey Jack cheese and the pico de gallo. Drizzle with sour cream. Top with guacamole.