1 Preheat oven to 400. 2  On a sheet pan drizzle squash with olive oil and lemon juice. 3  Sprinkle rosemary, garlic, salt and black pepper evenly over the squash then toss to coat. 4  Roast the seasoned squash in a preheated 400 oven for 20 minutes until just tender all the way through and starting to caramelize.ow to make it. 1  Preheat oven to 400. 2  On a sheet pan drizzle squash with olive oil and lemon juice. 3  Sprinkle rosemary, garlic, salt and black pepper evenly over the squash then toss to coat.