In a spice grinder, combine the coriander seeds with the cumin seeds, both cardamom seeds, cinnamon, nutmeg, and bay leaf, and process until finely ground. In a large bowl, combine the spice mix with the turkey, onion, cilantro, oil, ginger, and salt. Using your hands, mix until the meat is evenly seasoned and then cover the bowl with plastic wrap. Refrigerate the filling for 1 hour.
For the sauce: Heat a 12-inch cast iron skillet over high for 5 minutes. Add the tomatoes in a single layer, and cook, turning, until blackened on all sides, about 4 minutes. Transfer the charred tomatoes to a food processor, along with the cilantro, oil, garlic, peppercorns, and asafetida, and process until smooth. Scrape the sauce into a bowl and season with salt.
Line a baking sheet with parchment paper, and place a steamer insert into a large saucepan filled with 1 inch of water. Working with one wrapper at a time, place 2 teaspoons of the turkey filling into the center, and pull the wrapper up and around the filling, twisting and pleating it into a small topknot to seal. Place the momo on the prepared baking sheet, and cover with a clean kitchen towel. Repeat making momos with the remaining filling and wrappers.
To cook, spray the steamer insert with nonstick cooking spray and then bring the water to boil. Working in batches, arrange the momos in the steamer about 1 inch apart. Cover the pan and steam the momos until cooked through, about 5 minutes. Carefully remove the momos from the steamer, and transfer to a serving platter. Spoon some of the tomato-cilantro sauce onto the momos, and serve them while hot with extra sauce on the side.