Preheat broiler.

Gently break apart ground meat; sprinkle it in an even layer on a baking sheet. Combine granulated onion and garlic and salt, pepper, and cayenne; sprinkle evenly over meat and toss gently to combine. Divide meat into 16 2-ounce portions. Gently press each portion into a 2-inch biscuit cutter or ring mold to form uniform patties; use your thumb to make a slight indentation in the center of each patty.

Place a large cast-iron skillet or griddle over medium-high heat. When hot through, add burger patties and cook, turning once, to desired doneness; transfer to a paper towel-lined baking sheet and top with Cheddar slices. Place pan under broiler until cheese melts; do not burn.

Generously spread slider bun bottoms with Thousand Island dressing; add a layer of lettuce, a tomato slice, and a prepared cheeseburger patty. Add a generous dollop of Thousand Island dressing, top with slider bun tops, and serve hot.