In a large bowl mix turkey, egg, bread crumbs, garlic, onion, cilantro, spices and 1 teaspoon salt and pepper until combined, careful not to overwork the mixture. Roll meat mixture into 1-inch meatballs between palms of your hands, making 15 meatballs. Place on a baking sheet in rows of three and place in oven. Bake for 20-25 minutes or until 180 degrees internal temperature.
Bring a large, high-sided skillet or dutch oven to medium-high heat, add enchilada sauce and bring to a medium boil. Reduce temperature to medium and add meatballs then reduce to simmer and cook for 15-20 minutes.
In a small bowl, mash the avocados and add the reserved pickled jalapeno juice plus kosher salt to taste. Slice the rolls almost all the way in half and slather some of the mashed avocado on the buns. Top with pickled onion. Pour 1 tablespoon or so of enchilada sauce on the top half of the bun, then slice 2-3 of the meatballs in half and place on top of the avocados. Garnish with cilantro and cotija cheese plus pickled jalapeno if desired.