Preheat the oven to 425F. Half squash lengthwise, scoop seeds. Cut into thick wedges (leaving the skin on). Toss lightly with olive oil, salt and pepper. Roast, flipping halfway through until deeply caramelized.
Make the brown butter. Melt butter over medium heat. Add garlic and sage. Cook until butter smells nutty and turns golden brown.
To serve. Arrange squash on a platter or across plates. Spoon brown butter generously over the top. Sprinkle with orange zest, juice, toasted sunflower seeds and salt.