Heat the oven to 375°F and line a rimmed sheet pan with parchment. Sauté onion in oil for 6 minutes and cool for 5 minutes.
Soak oats in beer for 10 minutes. Stir in eggs, cooled onion, Worcestershire, paprika, salt, pepper and 2 tablespoons barbecue sauce.
Fold in beef and shape a 9-by-5-inch loaf about 2 1/2 inches high. Bake for 40 minutes.
Mix remaining 6 tablespoons barbecue sauce with vinegar and brush half over the loaf. Bake for 10 minutes.
Brush with the remaining sauce and bake for 5 to 15 minutes more until the center reaches 160°F, loosely covering if the glaze darkens too quickly.
Rest for 10 minutes and cut into 8 slices.