Preheat the oven to 325 degrees.
In a medium sauté pan, on medium-low heat, cook the onions, olive oil, salt, pepper, and thyme until the onions are 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 baking sheet. Spread the ketchup evenly on top.
Bake for 1 1/2 hours, until the internal temperature is 160 degrees and the meat loaf is cooked through. Serve hot, room temperature, or cold in a sandwich.
(A pan of hot water in the oven, under the meat loaf, will keep the top from cracking.)