1. Pierce potatoes all over with a fork and place in a shallow microwave-safe baking dish. Microwave on high, turning every 2 minutes, until tender, about 10 minutes total. Set aside to cool for 10 minutes.
2. In a skillet over medium-high heat, cook bacon until crisp, about 8 minutes. Transfer to a paper towel-lined plate to drain and cool. Crumble bacon.
3. Preheat oven to 400ºF. Halve potatoes lengthwise. Scoop out flesh into a large bowl, leaving shells of about 1/4-inch thickness. Place shells, cut sides up, on a baking sheet; bake until crisp, about 5 minutes.
4. Stir bacon, sour cream, tomatoes, scallions, salt and half of cheese into bowl with potato flesh. Spoon filling into shells, sprinkle with remaining cheese and return to oven. Bake until cheese is bubbling, about 10 minutes.