Cut steak across grain into 1/4-inch slices; cut slices into 1/2-inch-wide strips. Cut strips into 3-inch-long pieces. Combine steak pieces, 1/4 cup onions, sugar, soy sauce, garlic, and sesame oil.
Heat a 14-inch wok over high heat. Add 1 tablespoon canola oil to wok, swirling to coat. Add half of steak mixture to wok; stir-fry 2 minutes or until lightly browned. Spoon cooked steak mixture into a bowl. Repeat procedure with remaining 1 tablespoon canola oil and remaining steak mixture. Sprinkle with remaining onions and sesame seeds. Spoon 1/4 cup rice, about 2 tablespoons steak mixture, and 1 tablespoon kimchi onto each lettuce leaf; roll up. Serve immediately.