Place the dough on the pizza peel: When the oven is ready, dust a pizza peel with cornmeal or semolina flour, or do so on a baking sheet. (If you want to use a pizza stone but don’t have a peel, you can use a rimless baking sheet or the back of a rimmed baking sheet to slide it onto a stone, but the tree shape can be difficult to slide. A conveyor pizza peel works very well for larger trees like the one pictured.) Roll out the dough into a triangle shape, adding a small rectangle for a trunk. Place the dough on the pizza peel, or onto the baking sheet.
Quickly top the pizza: Spread a thin layer of pesto, then sprinkle with cheese. Add the “decorations” of red onions and peppers. Sprinkle with kosher salt.
Bake the pizza: Transfer the pizza to the pizza stone using the pizza peel, or place the baking sheet in the oven. Bake until the cheese is melted, about 5 to 7 minutes. Allow to cool slightly, then serve.