How to Make It
Line the bottom of the oven with a sheet of foil and preheat to 350°. Prick the sweet potato all over with a fork and roast directly on the oven rack for about 1 hour, until tender. Let cool slightly. Scrape the flesh into a bowl and mash well with a fork.
In a medium bowl, whisk both flours with the cornmeal and salt. In a stand mixer fitted with the paddle, beat 1 1/2 cups of the sweet potato puree (save the rest for later use) with the coconut oil until smooth. Gradually beat in the dry ingredients until a smooth dough forms.
Scrape the dough onto a work surface and gather into a ball; divide in half and pat into 6-inch disks. Wrap in plastic and refrigerate for 1 hour.
In a large skillet, heat the olive oil. Add the onion and cook over moderate heat, stirring occasionally, until just starting to brown, about 7 minutes. Add the tempeh, garlic and cumin seeds and cook, stirring, until fragrant and heated through, 3 to 5 minutes. Stir in the tomato puree, water, adobo sauce and oregano and cook for 2 minutes. Season with salt and let the filling cool completely.
Preheat the oven to 350° and line 2 large baking sheets with parchment paper. On a lightly floured surface, working with 1 disk at a time, roll out the dough 1/4 inch thick. Using a 4-inch round cutter, stamp out 10 rounds of dough. Moisten the edges with water and mound a scant 2 tablespoons of the filling on one half of each round; fold the dough over to form half-moons. Press the edges to seal and pleat at intervals or crimp with a fork. Transfer the empanadas to the prepared baking sheets. Repeat with the remaining dough and filling.
Bake the empanadas in the upper and lower thirds of the oven for about 25 minutes, until browned; shift the pans halfway through baking. Serve warm, with the Avocado Chimichurri.