In a bowl, whisk together fresh lime juice, olive oil, chopped cilantro, minced garlic, ground cumin, chili powder, salt, and pepper until well combined. Coat the flank steak evenly in this marinade. Cover and refrigerate for at least 30 minutes.

Cook rice according to package instructions for 15-20 minutes until fluffy. Heat black beans in a pot, seasoning as desired. If using corn, heat it as well.

Preheat grill or cast-iron pan over medium-high heat. Grill steak for 4-5 minutes per side until medium-rare (130°F). Let rest for 5-10 minutes before slicing.

Assemble bowls by layering cooked rice, black beans, corn, cherry tomatoes, avocado, and red onion. Top with sliced steak, feta cheese if using, cilantro, and lime wedges.