In a medium bowl, whisk together lime juice, olive oil, minced garlic, ground cumin, chili powder, salt, and black pepper. Coat the flank steak in the marinade, cover, and refrigerate for 30 minutes to 4 hours.

Cook rice according to package instructions (15-20 minutes). Heat black beans in a small saucepan over medium heat for 5 minutes. If using fresh corn, cook it in boiling water for 3-4 minutes or microwave frozen corn for 2-3 minutes.

Preheat grill to medium-high heat. Remove steak from marinade and grill for 4-5 minutes per side. Let rest for 5-10 minutes before slicing against the grain.

Assemble bowls with rice, black beans, corn, cherry tomatoes, red onion, avocado, and sliced steak. Optional: sprinkle with feta cheese and fresh cilantro.

Serve with lime wedges on the side to allow extra lime juice for added flavor.