Heat the oven to 350°F and cover a rimmed baking sheet with parchment paper or foil. The lined pan catches drippings and keeps cleanup from becoming the evening’s least appealing task.

Warm the olive oil in a medium skillet over medium heat, then cook the chopped onion for 5 to 7 minutes, stirring now and then; move it to a plate to cool. The onion should look translucent with light golden edges and smell sweet, not dark or bitter.

Place the ground beef, cooled onion, and remaining meatloaf ingredients in a large bowl, then combine with clean hands just until no streaks remain. The mixture should feel soft and tacky enough to hold together, without looking tightly compressed.

Set the mixture on the prepared baking sheet and form it into an even loaf about 8 inches long, 4 inches wide, and 3 inches tall; bake uncovered for 40 minutes. The loaf should hold a smooth mound shape as the surface begins to brown.

Stir the ketchup, white vinegar, brown sugar, garlic powder, and onion powder together in a small bowl. The glaze should be smooth, thick, and evenly blended with no pockets of brown sugar.

Coat the loaf with the glaze and continue baking for 20 minutes, checking the thickest center with an instant-read thermometer until it reads 160°F; rest before slicing. The glaze should look glossy and lightly caramelized, and the loaf should feel springy when gently pressed after its 10 to 15 minute rest.