Scrub and pierce the sweet potatoes several times with a fork. Microwave on a plate for 10 to 14 minutes, turning halfway, until a knife slides into every center; cook in two pairs if your microwave is small.
Meanwhile, heat the oil in a skillet over medium-high heat. Brown the beef and onion for 7 to 8 minutes, cooking the meat to 160°F.
Stir in tomato paste, paprika, garlic powder, 1/2 teaspoon salt and water. Simmer for 2 minutes until the mixture is moist and the onion is tender.
Mix the yogurt, lemon juice and remaining salt. Split the potatoes lengthwise and fluff the orange flesh with a fork.
Divide the beef among the potatoes, spoon the yogurt sauce over the top and add the chives.