In a medium bowl, whisk together fresh lime juice, olive oil, chopped cilantro, minced garlic, ground cumin, chili powder, salt, and black pepper. Add the flank steak, ensuring it's well coated in the marinade. Cover the bowl tightly and refrigerate for at least 30 minutes, or up to 4 hours.

While the steak marinates, cook the rice according to the package instructions, typically about 15-20 minutes for white rice. In a small saucepan, heat the rinsed black beans over medium heat for about 5 minutes.

Preheat your grill or grill pan to medium-high heat. Remove the steak from the marinade and grill for about 4-5 minutes per side until it reaches a medium-rare doneness.

Once grilled, transfer the steak to a cutting board and let it rest for 5-10 minutes. Then slice the steak against the grain into thin strips.

In serving bowls, add cooked rice as the base, then layer with black beans, corn, diced cherry tomatoes, and avocado slices. Top with sliced steak, feta cheese, and cilantro. Finish with lime wedges on the side.