Remove and discard stems and discolored spots from greens. Wash greens thoroughly; drain and tear greens into 1- to 2-inch pieces.
Sauté bok choy, next 3 ingredients, and, if desired, ginger in hot oil in a Dutch oven over medium heat 3 minutes or until onion is tender. Add greens, salt, and pepper; cook, stirring often, 5 minutes or until greens wilt. Cover and simmer 30 minutes.