• Prep the grill by making a charcoal fire.

TO PREPARE THE MINI BURGER PATTIES:

• Place ground beef in a large bowl. Lightly scramble egg and pour over beef. Sprinkle grated Parmesan, minced garlic, salt, and pepper over beef. Use hands to gently mix all ingredients until well-combined. Do not overmix or pack down, but the egg and seasonings should be evenly distributed throughout the beef.
• Use a ¼-cup measuring cup to scoop out the beef and gently roll into 20 balls. Press a cube of pepper jack into the center of each meatball. Carefully form the meat around the cube, making sure that the cheese is totally encased. Slightly flatten into patty with a 2-inch diameter. Repeat until all patties are formed. Set aside.

TO PREPARE THE MUSHROOMS:

• Place mushrooms and garlic in a large bowl. Pour melted butter over the top. Sprinkle with garlic salt and pepper. Gently mixed until all mushrooms are evenly coated. Layer two foil sheets on top of each other. Pour mushrooms into center of foil and bring up each side. Fold the top together and roll down several times. Repeat on each end until foil packet is tightly sealed.

TO GRILL:

• When grill is heated to medium-high, place foil packet of mushrooms on grill grate. Cook for 10 minutes.
• After mushrooms have been cooking for 10 minutes, flip foil packet over and move to the side (over indirect heat is fine) to make room for burgers. Brush grate with oil to prevent slider patties from sticking. Space patties out on grill and cook for 3 to 4 minutes or until nicely browned on the bottom. Use a spatula to flip patties and cook on the other side for about 4 more minutes or until meat is just cooked through. Transfer sliders to a platter and cover with foil to keep warm. Remove packet of mushrooms from the grill (whose total cooking time should have been 15 to 20 minutes), being careful of hot steam when you open the foil.

TO ASSEMBLE SLIDERS:

• Place a mini burger on the bottom half of a slider bun. Layer with avocado slices, spinach leaves, grilled mushrooms, and top bun. Skewer with a toothpick or bamboo pick to hold everything together.