Heat the oil in a large skillet over medium heat. Add the scallion whites and garlic and cook, stirring frequently, until soft, about 5 minutes. Sprinkle in the chili powder and cook, stirring, until the scallions are coated and the oil is brick red, about 1 minute. Remove from the heat and stir in the chicken, 1/2 cup of the salsa and 1/2 cup of the cheese. Set aside.
Halve the zucchini lengthwise and arrange cut-side down on a work surface. Use a Y-shaped vegetable peeler to shave off ribbons the entire length of each zucchini and as wide as possible (the first few may be too skinny). Make 36 zucchini ribbons total.
Lay out 3 ribbons, slightly overlapping to make a rectangle (think of this as your "tortilla"). Pile about 1/4 cup of the chicken mixture down along one of the short ends of the zucchini tortilla and then roll up to enclose the filling. Put in a 2- to 3-quart baking dish. Roll up the remaining zucchini ribbons and filling and arrange in the dish. Top the rolls with the remaining 1 cup salsa. Add several dashes of the hot sauce and sprinkle with the remaining 1/2 cup cheese.
Bake until the cheese is melted and the filling is hot, about 25 minutes. Let cool for a few minutes. Thin the sour cream out with a little water and drizzle over the enchiladas. Sprinkle with the reserved scallion greens and serve with more hot sauce if you'd like.
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