Heat the wok on high. When it is too hot to hover your hand an inch above the pan, add enough oil to coat the pan (at least a couple tablespoons, it should pool generously). Sizzle 4 slices of ginger until fragrant.
Add diced tomatoes and cook while stirring, until tomatoes have partly broken down.
Add the jar of suantang and 2 tablespoons of tomato paste and stir to combine. Bring to a boil, then lower heat to a simmer. Cook for several minutes to meld the flavors.
Transfer broth to your hotpot and top off with hot water or chicken stock. Add scallion whites, fresh or dried mushrooms and other flavoring ingredients as desired. Serve with desired hotpot spread.