To make the jammy zucchini: Heat the olive oil in a medium skillet over medium heat. Add the onion and salt. Cook for about 10 minutes, until the onion just starts to soften. Stir in the zucchini, cover, and cook for another 10 minutes. Remove the lid, lower the heat to medium low, and continue to cook, stirring occasionally, until the zucchini has broken down and is lightly caramelized, 25-35 minutes. Stir in the heavy cream and set aside until ready to use.
To make the pizza: While the zucchini is cooking, preheat an oven or grill (whichever you prefer for cooking pizza). Let the pizza dough rest, covered, at room temperature, while preheating and prepping.
Stretch the dough into a 12-inch circle. Place on a floured pizza peel, spread the jammy zucchini over the dough, and sprinkle with the mozzarella cheese. Bake until the cheese is bubbly and the crust is golden brown and cooked through. (The cook time will depend on your chosen pizza-making method.)
To serve: Once the pizza is cooked finish with black pepper before serving.