Preheat oven to 350 degrees.
Cook squash until fork tender, then mash and drain well. Mix with carrots, onion, soup, sour cream, mayo, cheese, and pepper.
Toss melted butter with dressing.
Spread a thin layer of dressing in a buttered 9x13 casserole dish or equivalent. Alternate layers of squash mixture and dressing mixture, ending with a thick layer of dressing mixture on top.
Bake at 350 degrees for 30 minutes. Allow to sit 5 minutes before serving.