Step 1

Heat a grill to medium-high direct heat and lightly oil the grates using a paper towel soaked in canola oil or nonstick grilling cooking spray.

Step 2

Spread a 16-inch-long piece of nonstick aluminum foil on a cutting board (or mist a piece of regular aluminum foil with nonstick cooking spray). Top with the onions, 1/4 teaspoon each salt and pepper and 1 tablespoon water. Bring two sides of the foil together, fold over twice to create a seal and then seal the remaining two ends. Put on the grill and cook for 12 minutes, flipping once. The onions should be tender with only a bit of charring. Carefully open the top of the foil to let all the steam out and continue to cook the onions, tossing, until browned and lightly charred, 3 minutes longer. Remove from the heat.

Step 3

While the onions cook, mix the ketchup and mustard together in a small bowl. Season with pepper and set aside.

Step 4

Lightly toast the English muffins on the grill and place one top and bottom on each of 4 plates. Spread some of the ketchup sauce on the bottom half of each muffin and top with a slice of tomato.

Step 5

Divide the beef into 4 patties about 4 inches in diameter and just under 1/2-inch thick. Sprinkle with a total of 1/2 teaspoon salt and 1/4 teaspoon pepper. Place the burgers on the grill. Cook until the edges of the burgers are browning, 3 to 5 minutes, and then flip. Brush the burgers with the remaining ketchup sauce and evenly top with the shredded cheese. Cover the burgers with the grill lid or a large heatproof bowl and continue to cook until the cheese has melted and the burgers are still a bit pink on the inside, about 3 minutes more.

Step 6

Put one burger on top of the assembled muffin bottom and top with some of the grilled onions and the top of the muffin. Serve with pickles if desired.