Preheat the oven to 375F/ 190C.

In a medium-large saucepan, saute the onion in 1 tbsp of the oil until it begins to soften. Add the garlic and continue to cook until fragrant. Add the mixture to a large mixing bowl. Set the pan aside to use again later.

Add the ground turkey and sausage and the next 8 ingredients (through the egg) into the mixing bowl. Mix by hand or use a spatula until everything is just combined. Shape the mixture into little meatballs, using the size of your sliders as a gauge as to how big to make them. (I like to use a small cookie scoop for this.) You should be able to get about 14-16 meatballs. At this point you can either move on to the next step and bake them right away or cover them in plastic wrap and chill until ready to use later that day.

Drizzle the rest of the olive oil directly over a medium sized sheet pan or line it with foil first, for easier clean-up. Place the meatballs on the pan, with about an an inch between each one. Bake the meatballs in the preheated oven for about 15-20 minutes. (They are done when the internal temperature registers 165F and a meatball in the center of the baking sheet is fully cooked inside when sliced in half.) Once they are done, heat the marinara in the same pan you used for the onions and carefully add the meatballs to the sauce. Bring to a simmer and cook just for a few minutes gently rolling the meatballs in the sauce.

Toast the buns if desired, then top the bottom half of the bun with 2 basil leaves, a meatball and a little bit of the sauce. Try not to put too much sauce or the buns get too soggy.) Place the other half of the bun on top and enjoy!