Preheat oven to 350 degrees F. Line a small baking sheet with parchment paper.
Place the beef and pork in a mixing bowl. Add the egg, breadcrumbs, pesto, salt, garlic powder, onion powder, pepper and half the Parmesan. Gently mix together to incorporate. Scoop out 24 heaping tablespoons meatball mix (each just shy of 1 1/2 tablespoons). Roll the mounds into round meatballs between your palms.
Place a large nonstick skillet over medium-high heat. Pour in the olive oil and heat until shimmering. Carefully add the meatballs to the skillet and fry until crispy and brown, 3 to 4 minutes on each side. Remove the meatballs from the skillet and discard any remaining oil.
Halve the potato buns horizontally without separating the buns from each other. Put the bottom buns on the prepared baking sheet and spread 1/2 cup marinara sauce on top. Line up the meatballs on top of the sauce, so that each bun will have its own meatball. Pour the remaining marinara sauce over the meatballs. Sprinkle with the basil. Lay the sliced provolone evenly over the meatballs. Place the top buns over the cheese.
Mix the melted butter and the garlic salt together. Generously brush over the top buns. Sprinkle the remaining Parmesan evenly over the butter mixture.
Bake until the provolone melts and the topping turns golden brown, about 15 minutes. Slice into individual sliders and serve immediately.