Make the marinade in a large baking dish: lime juice from 1 lime, garlic cloves, 1/4 cup onions, orange juice, olive oil, cilantro leaves, chopped onions and 1/2 tsp salt.
Add the beef to the marinade and cover with plastic wrap and refrigerate for an hour.
Take the strips out of the mojo marinade.
If using a grill outside, sear the strips over direct heat for 2 minutes per side (you will know the grill is hot enough when you can only hold your hand 5 inches above the grill grate for no more than 3 seconds). When using an indoor grill, once you see steam rising off the skillet, you are ready to grease it with a little fat and begin searing.
Sear the strips over direct heat for 2 minutes per side, then move them off the heat, cover, and cook and extra 4 minutes (or until desired doneness).
Once cooked, leave the strips to rest for 5 minutes.
Now make the lime yogurt side. Zest the second lime and then cut in half. Juice half the lime and cut the other half into wedges. In a small bowl stir together yogurt, lime zest and 1 TB lime juice. Season to taste with salt and pepper.
Separate and wash the romaine lettuce leaves.
Warm the tortillas for 30 seconds on each side in a dry skillet until toasty.
Set out the tortillas, romaine leaves, steak, 1/4 cup of onions, lime yogurt, lime wedges and mexican cheese blend. Let guests assemble their own fajitas.