In a mixing bowl, combine olive oil, minced garlic, ground cumin, chili powder, salt, and pepper. Rub marinade over flank steak and marinate for at least 30 minutes, or overnight for best flavor.

Bring 2 cups of water to a boil in a medium saucepan. Stir in rice, cover, and reduce heat to low; simmer for 18-20 minutes.

Preheat grill to medium-high heat. Grill marinated steak for 4-5 minutes per side until desired doneness. Let rest for 5 minutes before slicing.

In a large bowl, combine cooked rice, rinsed black beans, corn, diced tomatoes, red onion, and cilantro. Drizzle lime juice and toss to mix.

Slice steak thinly against the grain. Serve portions of rice mixture topped with steak slices.

Add avocado, shredded cheese, and sour cream or salsa as toppings before serving.