Step 1Heat a wok over high heat and add the canola oil, swirling it around in the wok to coat the pan. Heat until you see a wisp of smoke. Add the garlic and ginger and quickly stir-fry, only a few seconds, stirring with chopsticks.
Step 2Add the spinach stems and stir to coat the vegetables. Add 1 tablespoon hot water and cover the wok. Let the spinach stems steam for about 2 minutes, stirring once or twice and checking to make sure the vegetables don't burn. Add a little more water if necessary and a pinch of salt and black pepper.
Step 3Add the spinach leaves and stir as they wilt, about 30 seconds. Make a little well in the middle of the vegetables and add the fermented tofu. Stir over low heat until the tofu is completely incorporated and dissolves into the spinach. Serve immediately.