In a medium bowl, whisk together fresh lime juice, olive oil, chopped cilantro, minced garlic, ground cumin, chili powder, salt, and black pepper until fully combined. Add the flank steak and let marinate.

While the steak marinates, cook the rice according to package directions. Heat the black beans in a saucepan over medium heat for about 5 minutes. If using fresh corn, boil or sauté it briefly.

Preheat your grill to medium-high heat. Remove the steak from the marinade and grill for 4-5 minutes on each side for medium-rare. Let the steak rest for 5-10 minutes before slicing.

Divide the cooked rice between bowls, adding the warmed black beans and corn. Top with halved cherry tomatoes, sliced avocado, and thinly sliced red onion. Place sliced steak on top, sprinkle with feta cheese if desired, and garnish with extra cilantro and lime wedges.