Preheat grill to medium-high (or glance Stovetop Variation).
Mix onion, oil and 1 tablespoon ketchup in a medium saucepan. Duvet and cook dinner over medium-high warmth, stirring typically, except the onion is softened, 5 to 7 minutes. Decrease warmth to medium-low, utter and cook dinner, stirring as soon as in a while, except very soft, 5 to eight minutes extra. Switch to a medium bowl and let frigid for a jiffy.
Meanwhile, mix the remaining 1 tablespoon ketchup, mayonnaise, be pleased and vinegar in a runt bowl. Drawl aside.
Add beef, Worcestershire (or steak sauce) and pepper to the onion and gently mix without overmixing. Originate into 4 patties, about 3/4 go thick.
Oil the grill rack (glance Tip). Grill the burgers, turning as soon as, except an instant-read thermometer inserted within the center registers 165 degrees F, 4 to 5 minutes per side.
Assemble the burgers on toasted buns with the ketchup-mayonnaise sauce, tomato slices and lettuce.
Make Forward Tip: Put together ketchup-mayonnaise sauce (Step 3) and refrigerate for as a lot as 1 day.
Coat a nonstick pan, preferably solid-iron (or a grill pan), with cooking spray and warmth over medium-high warmth for 1 to 2 minutes. Add burgers, minimize warmth to medium and cook dinner, turning as soon as, except an instant-read thermometer registers 155°F (for pork and bison) or 165° (for beef or chicken), 4 to 5 minutes per side.
Tip: To oil a grill rack, oil a folded paper towel, care for it with tongs and rub it over the rack. (Pause not exhaust cooking spray on a sizzling grill.)