Preheat oven to 325 degrees F.
In a medium saute pan, over medium-low heat, cook the onions, olive oil, salt, pepper, and thyme until translucent, but not browned, approximately 15 minutes. Add the Worcestershire sauce, chicken stock, and tomato paste and mix well. Allow to cool to room temperature.
Combine the ground turkey, bread crumbs, eggs, and onion mixture in a large bowl. Mix well and shape into a rectangular loaf on an ungreased sheet pan. Spread the ketchup evenly on top. Bake for 1 1/2 hours until the internal temperature is 160 degrees F. and the meatloaf is cooked through. (A pan of hot water in the oven under the meatloaf will keep the top from cracking.) Serve hot, at room temperature, or cold in a sandwich.
