In a food processor, combine the first five ingredients for the sauce, pulse until coarsely pureed. Add the olive oil and pulse again until combined.
Drizzle olive oil into two 10" x 15" roasting pans. Divide the squash between the two pans, drizzle with more olive oil, toss to coat. Season with salt and pepper.
Roast squash 20 minutes. After 20 minutes, spoon pepper sauce over squash. You don't need to toss; thick areas of sauce will brown nicely.
Return to oven and roast until browned in spots and tender when pierced with a small sharp knife, 40-50 minutes longer. Serve hot, garnished with sliced scallions.