In a medium bowl, combine fresh lime juice, olive oil, chopped cilantro, minced garlic, ground cumin, chili powder, salt, and black pepper. Whisk until well combined to create a marinade.
Place the flank steak in a large resealable plastic bag or shallow dish and pour the marinade over it. Ensure the steak is well coated, then seal the bag or cover the dish.
While your steak marinates, cook rice according to package instructions. In a small saucepan, warm black beans until heated through, about five minutes.
Preheat your grill or grill pan over medium-high heat. Grill each side of the flank steak about 4-5 minutes or until it reaches your desired doneness.
Once cooled slightly, slice your steak against the grain into thin strips and assemble in bowls with cooked rice, black beans, corn, sliced steak, cherry tomatoes, avocado, red onion, and optional feta cheese.