In large bowl, combine egg and cornstarch; beat with wire whisk until smooth. Add beans, bread crumbs, cheese, 1 cup salsa, onions, garlic, salt, cumin and lemon juice; mix well. Shape into five 3 1/2-inch patties.
Heat oil in large skillet over medium heat until hot. Add patties; cook 14 to 16 minutes or until deep golden brown and centers are hot, turning once.
Place patties on bottom halves of buns. Top each with 1 tablespoon salsa. Cover with top halves of buns.