Preheat the oven to 200°C (400°F) with a rack in the centre. Line a baking sheet with foil.
Scrub the sweet potatoes and prick each one 6 to 8 times with a fork.
Bake on the tray for about 45 minutes, until a knife slides easily into the centre. In a hurry, microwave them on high for 8 to 10 minutes, turning halfway.
About 20 minutes before the potatoes are done, heat a large skillet over medium-high heat. Add the turkey and break it up, cooking until no pink remains and it reaches 74°C (165°F), about 6 minutes.
Add the black beans, diced tomatoes, chili powder, cumin and salt. Lower the heat to medium-low and simmer for 15 minutes, stirring now and then, until thick.
Split each sweet potato lengthwise and press the ends to open it up.
Fill with the chili and top with grated cheddar, a spoon of Greek yogurt and sliced green onion.