In a medium bowl, whisk together fresh lime juice, olive oil, chopped cilantro, minced garlic, ground cumin, chili powder, salt, and black pepper until well combined. Place the flank steak in a resealable plastic bag or shallow dish, pouring the marinade over it, ensuring the steak is well coated. Refrigerate for at least 30 minutes, or up to 4 hours for deeper flavor.

While the steak marinates, cook your rice according to package instructions, typically boiling it in water for about 15-20 minutes until fluffy. Meanwhile, heat black beans in a small saucepan over medium heat, seasoning them with a pinch of salt if desired. Stir occasionally, letting them warm through for about 5 minutes while the flavors meld.

If using fresh corn, bring a small pot of water to a boil and add the corn cobs, cooking them for about 5-7 minutes until tender. Alternatively, sauté your fresh corn in a skillet with a drizzle of olive oil for a golden touch. If you're using frozen corn, simply heat it in the microwave or in a pan for about 3-5 minutes, just until warmed.

Preheat your grill or grill pan to medium-high heat, about 400°F. Remove the marinated steak from the fridge, discarding the marinade. Grill the steak for 4-5 minutes on each side, achieving a beautifully charred exterior and medium-rare interior. Once cooked, transfer the steak to a cutting board and let it rest for 5 minutes to lock in the juices before slicing it thinly against the grain.

Start with a base of fluffy rice in each bowl. Layer on the warmed black beans, cooked corn, halved cherry tomatoes, diced avocado, and sliced red onion for freshness and crunch. Top each bowl generously with the grilled steak slices, adding crumbled feta cheese if desired. Finally, garnish with extra cilantro and lime wedges on the side for a zesty finish.