Heat your grill to high heat. Loosely form the beef into 4 large patties, about 3/4 inch thick and use your thumb to make an indent in the center of each one.
Rub each burger with 1 tsp of oil (on both sides.) Rub the remaining oil all over the sliced onion. Season with salt and pepper on both sides.
Place the burgers and onions on the grill and cook for 3 minutes. Flip and cook and additional 4 minutes (for medium rare) or until desired done-ness is reached. Remove from grill and cover to keep warm.
Place the bun, cut-side down onto the grill and cook until lightly charred, about 2-3 minutes. Once charred, cut into cubes to make the croutons.
Divide the lettuce, tomatoes, cheese and pickles between 4 bowls, followed by the burgers, onions and croutons.
In a medium bowl, stir together all the dressing ingredients until well mixed. Divide between the bowls.
Drizzle each bowl with some yellow mustard and DEVOUR!