1. Place oven rack on lowest shelf. If you have a stone, place it on rack. Preheat oven to 550°F, or your oven's highest temperature, for 45 minutes.
2. Warm a grill pan over medium-high heat. Drizzle 1 tsp. oil into pan. Add Canadian bacon and pineapple. Grill until meat and fruit are lightly marked on one side, about 3 minutes. Transfer to a cutting board and cut meat into bite-size pieces.
3. Dust a 14-inch-wide peel with cornmeal, then flatten dough on top. Using lightly floured fingers or a floured rolling pin, stretch dough into a 13- to 14-inch round. (Sprinkle peel with more cornmeal if necessary to make sure crust slides around easily on peel.) Brush remaining 2 tsp. oil over crust.
4. Sprinkle half of cheese over crust, leaving a 1-inch border. Arrange Canadian bacon, pineapple, remaining cheese and half of scallions on top.
5. Carefully slide pizza onto stone. Bake until crust is slightly charred on top and golden on bottom (lift an edge to check) and cheese has melted, about 8 minutes. Using peel, transfer pizza to a cutting board. Sprinkle remaining scallions over pizza. Let rest for a minute or 2, then slice and serve.