In a bowl, combine lime juice, olive oil, chopped cilantro, minced garlic, cumin, chili powder, salt, and pepper to create a marinade.
Place the flank steak in a resealable plastic bag and pour the marinade over it. Seal the bag and marinate in the refrigerator for at least 30 minutes, or up to 2 hours for more flavor.
Preheat your grill or grill pan over medium-high heat. Remove the steak from the marinade and let any excess marinade drip off.
Grill the steak for about 5-6 minutes on each side for medium-rare, or until your desired doneness is reached. Use a meat thermometer for accuracy (medium-rare: 135°F).
Once done, let the steak rest for about 5 minutes, then slice it against the grain into thin strips.
In serving bowls, layer the cooked brown rice at the bottom. Top with sliced steak, cherry tomatoes, diced avocado, corn, and red onion.
Drizzle any leftover marinade (if boiled for safety) or extra lime juice over the top for added flavor.
Serve immediately with lime wedges on the side.
Notes
For extra flavor, marinate the steak for up to 2 hours.