Warm the tablespoon of oil in a large skillet over medium heat. Add the onion and cook 3 to 4 minutes, until soft and translucent. Add the garlic for 30 seconds.
Add the crumbled tempeh, soy sauce, paprika and cumin. Cook 5 to 6 minutes, stirring now and then, until the crumbs are golden brown at the edges and smell nutty. Tip into a large bowl and let cool for 10 minutes.
Grate the sweet potatoes on the large holes of a box grater. Wring the shreds hard in a clean towel until only a few drops fall.
Add the sweet potato, green onions, eggs, flour, baking powder, salt and pepper to the tempeh. Mix until no dry flour shows. If it feels loose, add a tablespoon of flour.
Wipe out the skillet, add 2 tablespoons of oil, and heat over medium for about 2 minutes, until a shred of sweet potato sizzles on contact.
Scoop about 1/4 cup (60 ml) of mix per fritter, press into a patty about 1.5 cm (1/2 inch) thick, and slide into the oil. Flatten gently. Fit 4 in the pan without touching.
Fry 3 to 4 minutes per side, until deep golden and crisp. Turn once, when the crackle softens and the fritter lifts cleanly.
Push a thermometer into the middle of one fritter. It should read 71°C (160°F). If not, lower the heat and fry another minute per side.
Move the cooked fritters to a wire rack set over a baking sheet. Add oil between batches as needed.
Stir the yogurt, lime juice and salt together, spoon it on the fritters and scatter with chives.