Roll out the puff pastry on a lightly floured surface. Transfer to a 9-inch tart pan, pressing the pastry into the sides and bottom of the pan.
Prick the bottom of the pastry with a fork. Bake for 15 minutes, or until the pastry is golden brown.
While the pastry is baking, heat the olive oil in a large skillet over medium heat. Add the onions and garlic and cook until the onions are softened, about 5 minutes.
Add the oregano, basil, red pepper flakes, black pepper, and salt. Cook for 1 minute more.
Add the sausage and cook for 3 minutes. Add the tomatoes and cook for 2 minutes more.
Remove from heat and stir in the parsley.
To assemble the tart, spread the sausage and tomato mixture evenly over the crust. Sprinkle with the Parmesan cheese.
Bake for 15 minutes, or until the cheese is melted and the tomatoes are softened.
Let cool for 10 minutes before slicing and serving.
Interesting Facts
The tart can be served hot or at room temperature.
It can be made ahead of time and reheated.
Leftovers can be stored in an airtight container in the refrigerator for up to 3 days.