Preheat the oven: Preheat your oven to 375°F (190°C) and lightly grease a loaf pan or line it with parchment paper.

Prepare the mixture: In a large mixing bowl, combine the ground chicken, shredded horseradish cheddar cheese, chopped spinach, minced garlic, and breadcrumbs (if using). Add the egg, Worcestershire sauce, and season generously with salt and pepper.

Mix well: Using your hands or a spatula, mix all the ingredients together until evenly combined. Be sure the cheese and spinach are distributed throughout the chicken mixture.

Shape the meatloaf: Transfer the chicken mixture into the prepared loaf pan. Press it down evenly, shaping it into a loaf form.

Bake the meatloaf: Place the meatloaf in the preheated oven and bake for 35-40 minutes, or until the internal temperature reaches 165°F (75°C) and the meatloaf is fully cooked.

Rest and serve: Remove the meatloaf from the oven and allow it to rest for 5-10 minutes before slicing.