Preheat the oven to 400 degrees.
In a large mixing bowl, combine ground turkey, egg, breadcrumbs, salt, pepper, and minced red onion. Mix until just combined.
Lightly spray a casserole dish with non-stick cooking spray. *We used a 10.5x7.5” casserole dish as this was roughly the same size as the slider buns which made it easy to perfectly fit the turkey burger*
Scoop ground turkey into the casserole dish and use a spatula to spread to cover the bottom of the dish and smooth the top.
Place into the oven on the center rack and bake 12 minutes
Meanwhile, prepare garlic dill aioli. Combine ingredients in a small mixing bowl and whisk well.
Slice sliders in half and place cut side up. Scoop a spoonful of the aioli onto the top of each slider bun. Spread.
Remove turkey burger from the oven and lower the oven to 375 degrees.
Carefully lift the turkey burger out of the casserole dish and place onto cutting board.
Wipe the casserole dish clean, then add the bottom half of the slider buns and place turkey burger on top.
Cover the turkey burger with slices of mozzarella cheese, then add the top of the slider buns.
Brush the top of the buns with melted butter, then sprinkle with ranch seasoning.
Place back into the oven and bake for 10 minutes
Add your favorite toppings to the sliders and slice. Enjoy!