Wash the squash, chop of the ends, and evenly-slice.
Combine sliced squash, diced onion, sour cream, Duke's Mayonnaise, shredded cheddar cheese, and rosemary. Season, to taste, with garlic powder, black pepper, red pepper flakes, and kosher salt.
Pour the squash casserole mixture into a greased 9x13 pan.
Melt a stick of butter and mix it in with crushed RITZ crackers. Top the squash casserole mixture with the buttery cracker topping.