Pureed winter squash gives most of the body to these leaner cheesecake bars.
Preheat oven to 350°F. Coat a 9-by-13-inch baking pan with cooking spray
Process graham crackers, oats, 2 tablespoons sugar, 1/4 cup flour and butter in a food processor until finely ground. Add milk; pulse until completely moistened.
Transfer the graham cracker mixture to the prepared pan and evenly pat into the bottom. Bake for 10 minutes. Cool on a wire rack for 20 minutes.
Meanwhile, reduce oven temperature to 325°F. Beat both cream cheeses and the remaining 1/2 cup sugar in a large bowl with an electric mixer at medium speed until creamy, scraping down the sides occasionally. Beat in squash puree until smooth. Beat in eggs one at a time. Finally, beat in vanilla, cinnamon, salt and the remaining 3 tablespoons flour. Scrape the filling into the pan, spreading evenly over the crust.
Bake until set and the edges are light brown, about 35 minutes. Let cool completely on a wire rack, then refrigerate for at least 1 hour before cutting into bars.