In a large bowl, combine garlic, jalapeno, cilantro, chile powder, cumin, oregano, lime juice, orange juice, beer, and olive oil, whisking to combine. Add salt and pepper to taste (I added several pinches of salt here). Add steak to a baking dish or large bowl, and tuck slices of onion and orange between the layers of meat. Pour marinade over the meat, cover, and let rest for at least 4 hours (or up to 8 hours).
Take the steaks from the refrigerator, and let sit for 30 minutes before cooking. Meanwhile, prepare an outdoor grill (charcoal or gas) to high heat. Transfer steaks from the marinade to the grill in an even layer. Sprinkle each steak with a little salt and pepper. Grill the steaks for 1 minute per side, turning once, until about medium-rare. The steaks shown here are very thin, so the cook time is quick. Larger, thicker steaks may take longer. Remove the steak to a cutting board, let rest for 5 minutes, then chop into bite-sizes pieces.