Heat 1 Tbsp of the oil in a heavy pot over medium low heat. Add the mushrooms and sauté 1 minute, stirring constantly. Add 1 Tbsp of the soy sauce, then cook for another minute, continuing to stir constantly. Add the tomatoes, crab meat, and ginger. Cook for 4 minutes, constantly turning the mixture. Add the chicken stock, reduce heat to low, and cook for 15 minutes, stirring frequently. Stir in the remaining ingredients. Simmer for an additional 10 minutes. Serve hot crab soup in 4 big bowls.