Preheat the oven to 425°F.
In a large mixing bowl, toss the fennel together with the olive oil, salt, and sugar. Arrange the fennel in one layer on a parchment or foil-lined baking sheet. Bake in the oven for 20-25 minutes, until brown and tender. Set aside.
In the meantime, brown the sausage in a medium nonstick skillet over high heat, breaking up the pieces with your spatula to form small ½-inch chunks. Cook until fully browned on all sides and cooked through, about 8 minutes. Pour out some of the fat from the pan, and set the sausage aside.
Turn the heat up to 500°F.
On a floured cutting board or work surface, roll the pizza dough out, or use your fingers to stretch it. Line a baking sheet or pizza stone with parchment paper, and lightly brush it with oil. Place the dough on the sheet or stone, and press out the edges until the surface area is covered.
Spoon sauce over the dough and spread it in one even layer. Sprinkle the mozzarella cheese over the top, and arrange the sausage and fennel evenly on the surface. Sprinkle with some red pepper flakes if you want to up the heat.
Bake in the oven until the crust is brown and the cheese is melted, about 8-10 minutes. Return the pie to the cutting board, and sprinkle with the Parmesan cheese. Let rest for a minute, then cut into slices, and serve!