Toss the potatoes with 1 tablespoon of the oil, sprinkle with salt and pepper, and then spread out on one half of a baking sheet. Roast for 10 minutes. Meanwhile, toss the broccoli with the remaining 1 tablespoon oil and sprinkle with salt and pepper. Remove the baking sheet from the oven and spread out the broccoli in an even layer on the other half of the baking sheet. Return to the oven and roast until the potatoes are cooked through and the broccoli is just tender, another 5 minutes. Let cool slightly. Reduce the oven temperature to 375 degrees F.
Slice off the bottom third of the pizza crust to form a dome shape. Then, with a large biscuit cutter or pint glass, cut out the center of the dome, leaving a rainbow arc shape. Transfer the arc to a baking sheet. Cut 5 half-moon shapes from the scrap pieces of crust.
In a medium bowl, stir together the ricotta, mozzarella and Parmesan, and season with a pinch of salt and pepper. Spread the cheese mixture over the rainbow crust and the half-moons. Starting from the outside edge of the rainbow, fan out the pepperoni slices in a single line. Fan the diced bell pepper in an even line beneath the pepperoni. Then add lines of the squash, roasted broccoli and roasted potatoes.
Bake the pizza for 5 minutes, then add the half-moons to the bottom of each side of the rainbow to form clouds. Return to the oven and bake until the cheese and crusts are hot, about 10 minutes more. Serve immediately.