Preheat oven to 350°F (180°C) and line a rimmed baking sheet with parchment paper.
In a small bowl, whisk together ketchup, brown sugar, apple cider vinegar, and Dijon mustard. Set aside.
⅓ cup ketchup, ¼ cup packed dark brown sugar, 1 tablespoon apple cider vinegar, ½ teaspoon Dijon mustard
Heat olive oil in a skillet over medium heat. Add onions and cook for about 5 minutes until softened. Stir in garlic and cook for 1–2 more minutes. Let cool slightly.
1 tablespoon olive oil, ½ cup yellow onion, 1 clove garlic
In a large bowl, combine ground turkey, grated zucchini, feta, Italian seasoning, paprika, Worcestershire sauce, Dijon mustard, egg, salt, pepper, breadcrumbs, and the cooled onion mixture. Mix gently with your hands until combined.
1 tablespoon Italian seasoning, 1 teaspoon paprika, Salt and pepper, 1 tablespoon Worcestershire sauce, 1 tablespoon Dijon mustard, 1 large egg, 1 pound ground turkey, 1 cup zucchini, ½ cup feta cheese, ½ cup breadcrumbs
Shape the mixture into a loaf on the prepared baking sheet. Spread most of the glaze on top, letting it drip down the sides.
Bake for 45 minutes, brushing with reserved glaze during the last few minutes of cooking.
Let rest for 5 minutes, then slice and garnish with fresh parsley before serving.
Fresh parsley