Slice one apple using a mandoline slicer into 8 thin, 1/4 inch slices. Shred any remaining apple scraps and part of the second apple to get about 1/2 cup of shredded apple. Squeeze the shredded apple to remove excess moisture.

Preheat your outdoor grill to medium heat (350 to 375 degrees F or 175 to 190 degrees C).

In a bowl, mix the ground beef, breadcrumbs, 1 tablespoon of chili crisp, salt, and the shredded apple. Form this mixture into 4 patties, each about 1/2 inch thick and 4 inches in diameter.

Lightly oil your grill grate. Place the patties on the grill and cover. Carefully turn them halfway through cooking until they reach an internal temperature of 160 degrees F (71 degrees C), taking about 10 to 13 minutes.

While the patties grill, add the onion slices. Grill them, turning halfway, for about 8 to 10 minutes. Grill the apple slices for 4 to 5 minutes, turning halfway.

Toast the hamburger buns cut side down on the grill for 1 to 2 minutes if desired.

Once the onions are cool, separate them into rings. In a small bowl, mix the mayonnaise and the remaining 2 teaspoons of chili crisp together.

Spread the mayonnaise mixture on the buns, then stack them with the patties, grilled onions, and apple slices. Serve with extra chili crisp on the side.