Preheat oven to 400°F. Spray meatloaf pan with non-stick spray.
Heat olive oil in a large skillet over medium-low heat. Add the onion and cook, stirring occasionally, until softened; about 5 minutes. Add the garlic and cook until fragrant, about 1 minute. Stir in the mushrooms, a 1/2-teaspoon of salt, and a 1/4-teaspoon of pepper. Cook until the mushrooms give off their liquid and it boils away; about 10 minutes.
Transfer the onions and mushrooms to a large bowl, and then stir in the Worcestershire sauce and 3 tbsp of the sugar-free ketchup. Set aside to cool for 5 minutes.
Meanwhile, combine the breadcrumbs and milk in a small bowl.
Stir the breadcrumb mixture and the eggs into the mushrooms and onions. Using a fork or your hands, gently mix in the turkey, a 1/2 tsp of salt and a 1/4 tsp of pepper.
Pour the turkey mixture into greased meatloaf pan. Spread the remaining 4 tbsp sugar-free ketchup on top. Bake for 50 minutes.