Marinate the Steak:
In a small bowl, mix olive oil, lime juice, and all spices. Rub onto the steak and let sit for 15–30 minutes (or up to a few hours in the fridge).
Cook the Steak:
Heat a skillet or grill pan over medium-high heat. Cook steak for 3–5 minutes per side until desired doneness. Rest for 5 minutes, then slice against the grain.
Char the Corn:
In a dry skillet over high heat, cook corn for 2–3 minutes until lightly blackened. Stir occasionally.
Make the Sauce (Optional):
Stir together sour cream, lime juice, and chipotle. Add salt to taste.
Assemble the Bowls:
In each bowl, layer rice, steak, black beans, corn, lettuce, tomatoes, red onion, avocado, and cilantro. Drizzle with sauce and serve with lime wedges.