Heat 4 tablespoons of the olive oil in a large skillet. Add onions; cook, stirring often until caramelized. Season with salt and pepper; set aside.
Sprinkle 2 baking sheets with cornmeal. Divide dough in half; using hands or rolling pin, shape into 2 oblong crusts, each approximately 6 x 14 inches.
Spread pesto over each crust; top with onions. Sprinkle with cheese and walnuts. Brush edges with remaining oil.
Bake in the bottom third of oven at 450° F for about 18 minutes, or until crust is a deep golden colour. Cut each pizza into 8 pieces.