Preheat the oven to 450F or 425F convection. Line a baking sheet with parchment paper.
Place the squash on the baking sheet and drizzle the flesh with enough olive oil to lightly coat and sprinkle with salt. Rub the salt and oil all over the flesh and skin. Place cut-side-down on ½ of the baking sheet.
To make the meatballs, add all ingredients to a bowl and use your hands to mix thoroughly. Roll into 12 meatballs. Add the meatballs to the other half of the baking sheet and drizzle lightly with olive oil, then roll them around to coat in the oil.
Bake for 15-20 minutes, or until meatballs are cooked through and browned on the bottoms. Transfer the meatballs to a plate. Rearrange the squash so they are spaced evenly on the baking sheet. Reduce the oven to 400F and bake squash for 15-25 more minutes (depending on size) or until the inside flesh is cooked through and scoopable.
Flip the squash over. Let them cool for a bit so they’re easier to handle, if you’d like. Use a tablespoon to carefully scoop/shave out about 2 tablespoons worth of the flesh from each squash and transfer to a bowl (you end up with ½ cup worth). Stir in 1 cup marinara and milk until combined.
Sprinkle ½ cup of cheese into the cavity of each squash. Divide the marinara mixture between each squash, then nestle the meatballs into the mixture (three per squash). Spoon the remaining ½ cup marinara over top and sprinkle with parmesan. Bake for 10 minutes or until heated through.
Serve topped with herbs. Dig in with a knife and fork!