Prepare the Meatloaf Mixture:

1. Preheat the Oven: Preheat your oven to 350°F (175°C). Line a baking sheet with parchment paper or lightly grease a loaf pan.
2. Prepare the Vegetables: In a small skillet, heat a little oil over medium heat. Add the chopped onion and garlic, cooking for about 3-4 minutes until softened and fragrant. Set aside to cool.
3. Combine Wet and Dry Ingredients: In a large mixing bowl, combine the ground beef, egg, breadcrumbs, milk, Worcestershire sauce, dried oregano, thyme, salt, and pepper. Add the sautéed onion and garlic mixture to the bowl.
4. Mix the Ingredients: Using your hands or a spoon, gently mix all the ingredients together until just combined. Be careful not to overmix, as this can lead to a tough meatloaf.

Form and Bake the Meatloaf:

5. Shape the Meatloaf: Transfer the mixture into a loaf pan or shape it into a loaf on the prepared baking sheet. If using a baking sheet, be sure to shape it into a classic meatloaf form with slightly rounded edges.
6. Make the Glaze: In a small bowl, mix together the tomato sauce (or ketchup), brown sugar, and Dijon mustard (if using). Stir well to combine.
7. Glaze the Meatloaf: Brush the tomato sauce glaze generously over the top of the meatloaf, spreading it evenly with a spoon or spatula.
8. Bake the Meatloaf: Place the meatloaf in the preheated oven and bake for 45-50 minutes, or until the top is golden and slightly caramelized, and a meat thermometer inserted into the center reads 160°F (71°C).
9. Rest the Meatloaf: Once done, remove the meatloaf from the oven and let it rest for 10 minutes before slicing. This helps the juices redistribute and makes slicing easier.

Cut and Serve:

10. Slice and Serve: After resting, slice the meatloaf into 1-inch thick pieces. Serve with your favorite side dishes like mashed potatoes, roasted vegetables, or a fresh salad.