Place yellow onions, chorizo, green bell pepper, and garlic in a food processor; pulse until minced.
Transfer onion mixture to a large bowl. Add ground beef, ground pork, bread crumbs, eggs, ketchup, cumin, salt, and black pepper; mix with your hands until well-blended.
Form mixture into 12 patties.
Heat oil in a large skillet over medium heat. Cook patties in batches until browned and medium well done, about 5 minutes per side.
Serve cooked patties on hamburger buns topped with shoestring potatoes.
