Preheat and prep: Heat the oven to 375°F (190°C). Line a sheet pan with parchment or foil.
Lightly oil it to prevent sticking.
Sauté the aromatics: Warm the olive oil in a skillet over medium heat. Cook the onion with a pinch of salt until soft and translucent, 5–7 minutes. Stir in the garlic for 30 seconds.
Let cool slightly.
Soak the crumbs: In a large bowl, combine the breadcrumbs and milk. Let them sit 2–3 minutes to soften. This step keeps the meatloaf juicy.
Mix the meatloaf: Add the ground chicken, egg, ketchup, Dijon, Worcestershire, paprika, Italian seasoning, salt, pepper, parsley, and the cooled onion mixture.
Use a fork or your hands to gently mix until just combined. Don’t overwork the meat.
Shape the loaf: Transfer the mixture to the prepared pan. Shape into a loaf about 8–9 inches long and 4–5 inches wide. Smooth the top with damp hands.
Make the glaze: Stir together the ketchup, brown sugar, vinegar, and Worcestershire.
Spread half over the meatloaf.
Bake: Bake for 25 minutes. Brush on the remaining glaze and bake another 15–20 minutes, until the internal temperature reaches 165°F (74°C).
Rest and slice: Let the meatloaf rest 10 minutes before slicing. This helps it set and stay moist.
Serve: Pair with mashed potatoes, steamed green beans, or a simple arugula salad with lemon.