Pre-heat a cast iron skillet or grill on medium heat.
Slice your onions thin.
Grill up about ¼ of your onion and save the rest for another meal. When you are done grilling your onions, leave your grill pan on medium heat
Grab a large bowl.
Add your ground pork and Mexican chorizo.
Mix them together well making sure the ingredients are evenly mixed
Divide your meat mixture into 4, ½ pound patties. Alternatively you can make smaller patties if you like.
After you make your patties, make a deep dent in the middle of the burgers with your thumb. This will help them from inflating during cooking.
Add your burgers to your cast iron pan.
Cook for 4 minutes
Flip and cook for another 4 minutes.
After cooking, turn off the heat and add your cheese slices.
Add aluminum foil over your pan and let sit for a couple minutes to allow the cheese to melt.
While you are waiting, Add lettuce to the bottom of your hamburger buns. This prevents the bottom of the bun from becoming mushy when the burger is placed on it.
Remove the burgers from the pan and place on top of the lettuce on your hamburger buns.
Now add a tablespoon of Mayonnaise to each burger along with the grilled onions.