How to Make It
Preheat oven to 400°F. Rub cut sides of squash with 1 tablespoon oil; season with ¼ teaspoon salt and ½ teaspoon pepper. Place, cut sides down, on a baking sheet lined with parchment paper. Bake until tender when pierced with a fork, 25 to 30 minutes. Let cool for 10 minutes. Scrape out flesh with a fork (discarding skin), creating spaghetti-like strands.
While squash bakes, mix chicken, bread crumbs, Parmesan, parsley, egg, garlic, 2 tablespoons oil, and remaining ½ teaspoon each salt and pepper in a large bowl; shape into 16 balls.
Heat remaining 1 tablespoon oil in a large ovenproof skillet over medium-high. Working in 2 batches, cook meatballs, turning once, until browned, about 4 minutes total. Return all meatballs to skillet.
Pour marinara over meatballs and bring to a simmer over medium-high. Top with provolone and transfer to oven; bake until a thermometer inserted in the middle of a meatball registers 165°F and cheese is melted and bubbly, about 10 minutes. Garnish with parsley and serve with spaghetti squash.