In a small bowl, whisk together 1 tablespoon olive oil, 2 tablespoons lime juice, minced garlic, cumin, chili powder, salt, and pepper to create the marinade.
Place the flank steak in a resealable plastic bag or shallow dish, coat with the marinade, and refrigerate for at least 2 hours.
Preheat an outdoor grill or indoor grill pan to medium-high heat (approximately 400°F).
Remove steak from marinade and grill for 4 to 5 minutes per side for medium-rare, or until the internal temperature reaches 135°F (57°C).
Transfer the steak to a cutting board and allow it to rest for 10 minutes to retain juices.
In a large mixing bowl, combine the romaine lettuce, black beans, corn, cherry tomatoes, and red onion.
Whisk the remaining 1 tablespoon olive oil and 1 tablespoon lime juice together; toss the salad components with this mixture.
Slice the rested steak thinly against the grain.
Divide the salad base among four plates, top with steak slices and avocado, and garnish with fresh cilantro.