In a bowl, mix olive oil, minced garlic, ground cumin, chili powder, salt, and pepper. Rub this mixture over the flank steak and let it marinate for at least 30 minutes or preferably overnight.

Bring 2 cups of water to a boil in a saucepan. Add 1 cup of rice, cover, and let it simmer on low heat for 18-20 minutes until fluffy.

Preheat your grill to medium-high. Grill the marinated flank steak for 4-5 minutes on each side, or until cooked to your preference. Allow to rest for 5 minutes before slicing.

In a large bowl, mix the cooked rice with black beans, corn, diced tomatoes, red onion, cilantro, and lime juice until well combined.

Thinly slice the rested steak against the grain and layer it over your rice mixture in serving bowls.

Garnish each bowl with slices of avocado, a sprinkle of cheese, and a dollop of sour cream or salsa. Serve immediately.