Preheat a grill pan or skillet over medium-high heat until just barely smoking.
Combine garlic powder, chili powder, kosher salt, paprika, and cumin in a bowl; rub over all sides of flank steak.
Grill flank steak in the preheated grill pan, flipping halfway through, until browned and cooked to desired doneness, about 8 minutes. Let steak rest on a work surface for 10 minutes. Thinly slice steak against the grain.
Divide rice, tomatoes, romaine lettuce, tortilla chips, black beans, jalapeno peppers, and lime wedges between 2 serving bowls; top with steak, cotija cheese, and 1 tablespoon cilantro.
Combine avocados, water, 1/2 cup cilantro, sour cream, lime juice, garlic, and salt in a blender; blend until dressing is smooth. Pour dressing over each bowl.