Combine the mayonnaise and hatch chile sauce and mix well. Set aside.
Cooking the toppings
In a sauté pan heat the bacon on medium high heat and cook until done, about 5-10 minutes depending on the thickness of the bacon. Pat the grease off and set aside.
Heat a sauté pan over medium high heat and add the olive oil. Add the onions and cook until they have turned translucent. Reduce the heat to medium and continue to cook until they start turning a nice caramel brown color and have softened.
Making the hamburger
In a mixing bowl combine the ground beef, salt and hatch peppers together. Be sure to not overmix.
Form into 4 balls and then flatten to about a half an inch. If you want a larger burger flatten a bit more.
On medium high/indirect heat, cook the hamburgers for 3-5 minutes per side depending on preferred doneness. Place the slice of cheese on top of the burger after it has been flipped and allow to melt.
Assembly
Spread hatch chile mayonnaise on the bottom bun and top with the burger patty. Add the bacon and caramelized onions and spread a little more hatch mayonnaise on the top bun if desired.