Preheat the oven to 350 degrees F (175 degrees C).Advertisement
Slice ends off zucchini and cut them lengthwise. Scoop out centers, leaving a 1/4-inch wall around each. Line up zucchini "boats" on a rimmed baking sheet.
Heat olive oil over medium-low heat in a large saucepan. Add onion and bell pepper; cook and stir until onion is softened and translucent, about 5 minutes. Remove from heat; stir in cooked chicken, cream cheese, and taco seasoning until well combined and creamy.
Spoon chicken mixture evenly into zucchini boats. Pour enchilada sauce over each, making sure to cover any exposed zucchini and barely cover the bottom of the baking sheet. Top each with Cheddar cheese.
Bake in the preheated oven until cheese is just starting to brown, about 25 minutes. Let cool for 5 minutes before serving.
If you don't have cooked chicken on hand, cut boneless, skinless chicken breasts into bite-sized pieces and add to the saute pan a few minutes after starting the onions/peppers. Cook until no longer pink in the center.