In a small bowl, mix brown sugar, chili powder and salt. Rub onto both sides of steak., Place peppers and onion on a grilling grid; place on grill rack over medium heat. Grill, covered, until crisp-tender, stirring occasionally, 9-11 minutes; add tomatoes during the last 2 minutes. Remove from grill., Place steak and corn directly on grill rack; close lid. Grill steak until a thermometer reads 135° for medium-rare, 8-10 minutes on each side; grill corn until lightly charred, turning occasionally, 10-12 minutes., Divide greens and cilantro among 4 bowls. Cut corn from cobs and thinly slice steak across the grain; place in bowls. Top with vegetables; drizzle with vinaigrette. If desired, serve with cheese, lime and tortillas.