Preheat oven to 425°F. Cut squash into 1 1/2"-thick wedges, leaving skin on. Scrape off seeds and strings with a large spoon and discard. Coat wedges with 3 tablespoons oil and season with salt and pepper. Lay wedges cut side down on a large rimmed baking sheet. Roast, carefully turning halfway through, until golden brown on both sides, about 30 minutes.
Heat remaining 1 tablespoon oil in a small skillet over medium-high heat. Add pecans and cook, swirling pan often, until seeds are brown, 4–5 minutes. Transfer to paper towel, Sprinkle with salt
Transfer squash to a large platter and drizzle with balsamic vinegar. Sprinkle squash with torn mint leaves and toasted pecans.