Preheat your oven to 350°F (175°C).

In a large mixing bowl, combine the lean ground turkey, egg, chopped onion, Italian-style breadcrumbs, milk, Worcestershire sauce, salt, and ground black pepper.

Transfer the meat mixture to a greased 9x5 inch loaf pan or form it into a loaf shape on a baking sheet.

In a small bowl, whisk together the ketchup, brown sugar, and prepared mustard for the glaze.

Spread the glaze generously over the meatloaf.

Bake in the preheated oven for about 1 hour, or until the internal temperature reaches 165°F (74°C).

Let it rest for 10 minutes before slicing.

Serve warm, optionally with mashed potatoes or a green salad.