Preheat the oven to 400°F and spread 1/4 cup of the enchilada sauce over the bottom of a 13 x 9-inch baking dish.
Trim the zucchinis and slice each lengthwise into 6 slices (12 total) about 1/4-inch thick, using a mandolin or sharp knife for even slices.
Season both sides of the zucchini slices with 1/2 teaspoon kosher salt and black pepper to taste.
Heat a grill pan over high heat and brush or spray lightly if desired; grill zucchini slices about 2 minutes per side until pliable with grill marks but not fully cooked.
Meanwhile, heat 1 teaspoon olive oil in a medium skillet over medium-high heat. Add the minced onion and garlic and sauté about 2 minutes until softened.
Add the shredded chicken, 1/4 cup enchilada sauce, 1/4 cup chopped cilantro, 1 teaspoon cumin, 1/2 teaspoon dried oregano, and 1/4 teaspoon chipotle chili powder to the skillet; cook 4–5 minutes until heated through and combined, then remove from heat.
Spoon about 3 tablespoons of the chicken mixture onto the end of each zucchini slice, roll up tightly, and place each roll seam-side down in the prepared baking dish.
Pour the remaining enchilada sauce over the arranged roll-ups, sprinkle evenly with the shredded Mexican cheese blend, and cover the dish tightly with foil.
Bake for 20 minutes, or until the cheese is melted and hot. Remove foil for the last few minutes if you prefer lightly browned cheese.
Drizzle with sour cream if desired and garnish with additional chopped cilantro before serving.
