On the grill or under the broiler, roast the jalapeno peppers whole, until they start to turn black. Once they are black on all sides, put into a brown paper bag, close and let sit 5 minutes. Remove from bag and peel off skin.
Using a knife, slit open jalapenos, and take the seeds out and remove the stem. Cut jalapenos in half so you have 4 total slices of jalapeno. Set aside.
In a bowl combine ground beef, 1 egg, ketchup, salt, garlic, and onions. You may also use any other seasonings you like in your hamburger mixture. Mix well.
Form 8 thin patties. Take one slice of jalapeno and one slice of pepper jack cheese and place on 4 of the patties. Top each patty with remaining four patties and seal the edges together so the cheese doesn't leak out.
Grill burgers or cook as usual until done. Your burgers will have a spicy, cheesey surprise in the middle of each one. Delicious!