Prepare butternut squash by peeling, 1 inch cubing, and steaming or simmering in water until fork tender. Set aside and allow to cool to room temperature. Meanwhile, preheat oven to 350°F. Lightly grease half sheet pan with pan spray.
In a large bowl with paddle attachment, combine flour, sugar, baking powder and salt on low until well combined. In another bowl, mash butternut squash until no lumps and combine with milk, oil and vanilla. Add wet ingredients to dry and mix on low for about 3 minutes. Hand fold in chocolate chips.
Pour batter onto sprayed sheet pan and bake for 30 - 35 minutes or until a toothpick inserted comes out clean. Remove pan from oven and allow to cool to room temperature before cutting.