Healthy Grilled Cheeseburger Recipe:

Ingredients:

Canola oil or nonstick grilling cooking spray, for oiling the grates

1 medium red onion, thinly sliced

Kosher salt and freshly ground black pepper

2 tablespoons ketchup 

2 tablespoons yellow mustard

4 whole wheat English muffins, split

1 medium ripe tomato, cored and cut into 4 thick slices

1 pound 90-percent lean ground beef 

2 ounces 50-percent reduced-fat sharp Cheddar, grated (about 1/2 cup)

Pickles, for serving, optional

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