Preheat oven to 425 degrees. Rub the skins of the potatoes with 1 t. of the oil. Place on the middle rack o the oven and bake until fork-tender, 45-50 minutes.
Meanwhile, heat the remaining 3 teaspoons oil in a nonstick saucepan over medium heat. Add the onion and garlic and cook, stirring occasionally, until golden, 8-10 minutes. jAdd the tomatoes, zucchini chili powder, and cumin; bring to a boil. Reduce the heat and simmer, covered, until the zucchini is tender, about 15 minuts. Add the chicken and hat through.
Cut the potatoes in half lengthwise and spoon the chili evenly over the halves. Top each half with 1 T. of the sour cream and sprinkle with the cilantro.