Preheat your oven to 350°F (175°C) and grease a loaf pan or line it with parchment paper.
In a large mixing bowl, combine the ground beef, onion soup mix, breadcrumbs, egg, milk, diced onions, minced garlic, thyme, Worcestershire sauce, salt, and pepper.
Mix the ingredients together gently until just combined. Avoid overmixing to keep the meatloaf tender.
Transfer the mixture into the prepared loaf pan, shaping it evenly.
Spread the ketchup on top of the meatloaf for a glaze.
Bake in the preheated oven for about 1 hour, or until the internal temperature reaches 160°F (70°C).
Remove from the oven and let the meatloaf rest for 10 minutes before slicing.
Notes
Slice the meatloaf and serve on a warm plate with a sprinkle of fresh parsley for color. Pair it with mashed potatoes or a side salad for a complete meal.