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 1 tsp. oil in a skillet over medium-high heat. Crumble sausage into skillet; sauté until no longer pink, 3 minutes. Transfer to a plate.
3. Dust a 14-inch-wide pizza peel with cornmeal; 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 surface of crust.
4. Arrange cheese over dough, leaving a 1-inch border. Spoon sauce in a spiral over pizza, getting a little bit on cheese, leaving a 1-inch border. Sprinkle on sausage, jalapeño and red onion.
5. Carefully slide pizza onto stone. Bake until crust is just 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. Let rest for a minute or 2, then slice and serve.