Step 1: Prepare the Steak Marinade. In a shallow dish or a large zip-top bag, whisk together lime juice, olive oil, minced garlic, 1/4 cup chopped cilantro, cumin, chili powder, salt, and pepper. Add the flank steak, ensuring it is fully coated. Marinate for at least 30 minutes at room temperature, or up to 4 hours in the refrigerator. Do not marinate for more than 4 hours as the acid can toughen the meat.
Step 2: Cook the Cilantro Lime Rice. In a medium saucepan, combine the rinsed rice and water (or broth). Bring to a boil, then reduce heat to low, cover, and simmer for 15-18 minutes, or until all liquid is absorbed and rice is tender. Once cooked, remove from heat, let it sit for 5 minutes, then fluff with a fork. Stir in 1/4 cup fresh lime juice and 1/2 cup chopped cilantro. Season with salt to taste.
Step 3: Prepare the Toppings. While the steak is marinating and rice is cooking, prepare all your desired toppings: dice the avocados, slice the red onion and cherry tomatoes, and rinse and drain the black beans and corn. Set aside.
Step 4: Sear the Steak. Heat a cast-iron skillet or heavy-bottomed pan over medium-high heat until very hot. Add a tablespoon of high-smoke-point oil. Remove the steak from the marinade (discarding excess marinade) and sear for 3-5 minutes per side for medium-rare, or to your preferred doneness. Achieve a nice crust on the outside. Let the steak rest on a cutting board for 5-10 minutes before slicing thinly against the grain.
Step 5: Assemble the Bowls. Divide the cilantro lime rice among 4 bowls. Top generously with the sliced steak, black beans, corn, diced avocado, cherry tomatoes, and red onion. Garnish with extra fresh cilantro, a squeeze of lime juice, and any other desired toppings like sour cream or hot sauce. Serve immediately and enjoy your delicious cilantro lime steak bowls!