Preheat the oven to 475 degrees F. Thinly slice each cube of butternut squash and toss in a small bowl with the olive oil. Thinly slice the onion and sage.
Sprinkle a work surface with the cornmeal and use a rolling pin and/or your hands to stretch the dough into a 12-inch circle. Spray a baking sheet with cooking spray and place the dough onto it.
Crumble the gorgonzola and sprinkle it evenly all over the dough, leaving a 1-inch border for the crust. Scatter the squash and onion on top of the cheese. Sprinkle the sage on top.
Bake until the cheese is melted, the squash is softened and the crust is almost browned, about 11 minutes. Scatter the walnuts over the pizza and bake until they are lightly toasted, an additional 2 minutes. Slice the pizza into 8 wedges.