Prep the oven and pan: Heat the oven to 350°F (175°C). Line a rimmed sheet pan with foil and place a wire rack on top if you have one. Lightly oil the rack. This helps fat drip away and keeps the loaf from getting soggy.

Soften the aromatics: In a small skillet, warm olive oil over medium heat. Sauté the onion with a pinch of salt for 4–5 minutes, until translucent. Add garlic and cook 30 seconds more. Let cool slightly. This step mellows the bite and boosts sweetness.

Hydrate the oats: In a large bowl, combine oats and milk. Let sit 5 minutes. The oats will swell and become tender, improving the final texture.

Build the mixture: Add the egg, ketchup, Worcestershire, salt, pepper, Italian seasoning, and smoked paprika to the bowl with the oats. Stir until well combined, then fold in the cooled onion and garlic.

Add the meat: Crumble the ground beef into the bowl. Using clean hands, gently mix until just combined. Do not overwork it, or the loaf can turn dense.

Shape the loaf: Transfer the mixture to your prepared pan. Shape into a tight loaf about 8 inches long and 4 inches wide, smoothing the top and sides for even cooking.

Mix the glaze: Stir together ketchup, brown sugar, mustard, and vinegar. Spread half over the top and sides of the loaf.

Bake: Place in the oven and bake for 35 minutes. Remove, brush on the remaining glaze, and return to the oven for 15–20 minutes, until the center reaches 160°F (71°C).

Rest and slice: Let the meatloaf rest for 10 minutes before slicing. This keeps the juices where they belong and makes clean slices.

Serve: Pair with mashed potatoes, roasted carrots, or buttered peas. Spoon any pan juices over the slices for extra flavor.