How to Make It
Heat the oven to 400°. Put the squash slices in a large bowl, season with salt and black pepper, and drizzle with enough olive oil to coat. Toss the squash with your hands to distribute the seasoning, then transfer to two baking sheets and spread out the slices. Roast until the squash is cooked through and the edges are browned here and there, about 15 minutes. (You can roast the squash up to 3 hours in advance and hold it at room temperature.)
Arrange the squash on a warm platter or on individual plates, then quickly make the brown butter sauce: Melt the butter in a small skillet over medium-high heat. Add the crushed red pepper and sage, season with a little salt and black pepper, and whisk the butter and aromatics as the butter begins to bubble and brown. When the butter is foamy and nutty-smelling, in a minute or so, spoon it over the squash. Garnish with a few arugula leaves or chopped parsley and use a sharp vegetable peeler to shave Parmesan over the squash. Serve with lemon wedges.