Prep your pan and oven: Heat the oven to 375°F (190°C). Lightly oil or spray a 9x13-inch baking dish.
Spoon 2–3 tablespoons of enchilada sauce into the bottom and spread it thinly to prevent sticking.
Sauté the aromatics: In a large skillet over medium heat, warm the oil. Add onion and a pinch of salt. Cook for 3–4 minutes until translucent.
Stir in garlic and jalapeño (if using); cook 30 seconds until fragrant.
Cook the zucchini: Add the zucchini, cumin, chili powder, and oregano. Cook 4–6 minutes, stirring occasionally, until the zucchini softens but still has a little bite. Season with salt and pepper.
Add the chicken and sauce: Stir in the shredded chicken and about 1/3 cup of enchilada sauce to moisten the mixture.
Warm through for 1–2 minutes. Turn off the heat and add the lime juice and half the cilantro. Taste and adjust seasoning.
Warm the tortillas: To prevent cracking, wrap tortillas in a damp paper towel and microwave for 30–45 seconds, or briefly heat them in a dry skillet.
Keep covered to stay pliable.
Fill and roll: Place a tortilla on a work surface. Spoon 2–3 tablespoons of the chicken-zucchini filling down the center. Sprinkle with a little cheese.
Roll tightly and place seam-side down in the prepared dish. Repeat with remaining tortillas and filling.
Top with sauce and cheese: Pour the remaining enchilada sauce evenly over the rolled tortillas. Use just enough to coat; you don’t want a soup.
Sprinkle the rest of the cheese on top.
Bake: Bake uncovered for 15–18 minutes, until the cheese is melted and bubbling and the edges are lightly golden.
Finish and serve: Let the enchiladas rest for 5 minutes to set. Garnish with the remaining cilantro and any extra toppings you like. Serve with lime wedges.