Arrange beef on a platter; spinach, mushrooms, bamboo shoots, cabbage, and onions on another platter; and tofu on a third platter or with the vegetables.
Combine soy sauce, lemon juice, and 1/2 cup chicken broth in a bowl; portion dipping sauce into 6 very small bowls.
Pour remaining broth into a saucepan and bring to a boil. Transfer hot broth to a fondue pot.
Serve with chopsticks or forks. Individuals cook their own portions of meat, vegetables, and tofu in the boiling broth, then dip in dipping sauce and eat.
