In a medium bowl, whisk together lime juice, olive oil, cilantro, garlic, cumin, chili powder, salt, and pepper until smooth.

Place the flank steak in a resealable bag or shallow dish and pour the marinade over it. Seal and refrigerate for at least 30 minutes.

Prepare the rice according to package instructions.

Warm black beans in a small saucepan over medium heat for about 5 minutes. Stir occasionally.

Cook fresh corn by boiling or sautéing until tender, about 5 minutes, or microwave frozen corn until warmed.

Preheat grill or grill pan to medium-high heat, about 375-400°F.

Grill the marinated flank steak for about 4-5 minutes on each side until medium-rare, reaching an internal temperature of 130°F.

Let the steak rest for 5-10 minutes before slicing against the grain into thin strips.

In serving bowls, layer rice, black beans, corn, sliced steak, tomatoes, avocado, and onion, then top with feta if desired.