In a bowl, combine olive oil, chili powder, cumin, garlic powder, onion powder, salt, pepper, and lime juice. Whisk until well blended. Add the flank steak and marinate for at least 30 minutes, or up to 2 hours in the refrigerator for more flavor.
Preheat a grill or grill pan over medium-high heat. Remove the steak from the marinade and grill for about 5-7 minutes on each side, or until it reaches your desired doneness. Let the steak rest for 5 minutes before slicing it thinly against the grain.
While the steak is resting, prepare the bowls. In each bowl, layer 1/4 cup of cooked brown rice, 1/4 cup of black beans, 1/4 cup of corn, and a handful of cherry tomatoes.
Top each bowl with sliced steak, avocado, and a sprinkle of fresh cilantro. Serve with lime wedges on the side.