In a small bowl, combine lime juice, lime zest, chopped cilantro, olive oil, cumin, paprika, garlic powder, salt, and pepper to create a marinade. Place the flank steak in a zip-lock bag and pour the marinade over it. Seal the bag and let it marinate in the refrigerator for at least 30 minutes (or up to 2 hours for maximum flavor).
In a medium saucepan, combine jasmine rice with 2 cups of water and a pinch of salt. Bring to a boil, cover, and reduce heat to simmer for 15 minutes, or until water is absorbed and rice is tender. Fluff with a fork and set aside.
Heat a grill pan or outdoor grill over medium-high heat. Remove the steak from the marinade and discard the marinade. Grill the steak for about 3-5 minutes on each side for medium-rare, or to your desired doneness. Remove from heat and let it rest for 5 minutes before slicing it against the grain.
In each bowl, add a scoop of jasmine rice, followed by a portion of black beans and corn. Top with sliced steak, avocado, and cherry tomatoes. Drizzle with extra lime juice if desired.
Finish each bowl with a dollop of sour cream if using, and sprinkle with additional cilantro for garnish.