Drain the tofu on paper towels. Heat 1 tablespoon of the oil over medium-high heat in a wok or a large, heavy lidded skillet and add the tofu. Stir-fry until golden brown and remove from the heat.
Combine the shallot or onion and the ginger in a food processor or mini-chop and blend until finely minced, almost a paste.
Heat the remaining oil over medium-high heat in a wok or skillet and add the cumin seeds, fennel seeds and whole chilies. Cook, stirring, for about 15 seconds, or until the spices are fragrant and reddish-brown. Add the onion and ginger and stir-fry until it is lightly browned, about 3 minutes. Add the coriander, salt, cayenne and turmeric, stir for about 10 seconds and add the spinach in batches, adding the next batch after the first batch wilts and stirring and scraping the bottom of the pan to deglaze.
Stir in the tofu, cover, reduce the heat to medium-low and simmer, stirring occasionally, for 2 to 3 minutes, until the spinach is uniformly wilted and the tofu is warmed through.
Whisk the cornstarch into the yogurt. Remove the pan from the heat, remove the chilies, and stir in the yogurt. Taste, adjust salt and serve with rice or other grains.