Grate the onion and carrot using a box grater. Gently squeeze excess liquid from the grated onion using a clean kitchen towel or fine-mesh strainer. The vegetables should remain moist but not dripping wet.

To the bowl, add the ground beef, onion, carrot, garlic, egg, oats, tomato paste, Worcestershire sauce, thyme, paprika, salt, and black pepper. Mix gently until just combined, being careful not to overmix. The mixture should be moist but hold together. If excessively wet, add 1–2 additional tablespoons of oats.

Let the mixture sit for 5–10 minutes to allow the oats to absorb excess moisture from the grated vegetables.

Spoon the mixture into the prepared 9 × 5-inch loaf pan, spreading it evenly and gently pressing it into the corners without packing it too tightly. Smooth the top with a spatula.

In a small bowl, whisk together ketchup, balsamic vinegar, and Dijon mustard. Spread evenly over the top of the meatloaf.

Bake uncovered for approximately 55–65 minutes, or until the centre reaches an internal temperature of 160°F (71°C). Because the grated vegetables release moisture during cooking, some liquid may accumulate around the edges of the pan.

Allow the meatloaf to rest in the pan for 10 minutes before carefully draining any accumulated liquid. Lift the meatloaf out using the parchment overhang or carefully transfer it to a cutting board. Slice and serve.