In a medium bowl, whisk together fresh lime juice, olive oil, chopped cilantro, minced garlic, ground cumin, chili powder, salt, and black pepper. Coat the flank steak thoroughly with this zesty marinade. Cover and refrigerate for at least 30 minutes or up to 4 hours.

While the steak marinates, cook rice according to package instructions, usually about 15-20 minutes. Heat black beans over medium heat for roughly 5 minutes and season with salt and pepper. Set aside.

Cook the corn by boiling it for about 3-5 minutes or sautéing in a skillet until just tender, about 4-6 minutes.

Preheat your grill or grill pan to medium-high heat. Grill the steak for 4-5 minutes per side, aiming for medium-rare doneness. Let rest for 5-10 minutes before slicing.

In a serving bowl, add a generous scoop of the cooked rice as the base. Layer in warmed black beans, cooked corn, halved cherry tomatoes, diced avocado, and red onion. Finally, slice the rested steak and arrange it over the top. Sprinkle feta cheese if desired.

Finish with a sprinkle of extra chopped cilantro and serve with lime wedges on the side. Squeeze lime juice over the bowls to enhance flavor.