Preheat oven to 400°F. Line a sheet tray with parchment paper, set aside.
On a lightly floured surface with a rolling pin, carefully roll out the thawed sheet of puff pastry into a rectangle approximately 10 by 14 inches long. Transfer to the prepared sheet tray.
With a paring knife, lightly mark a 1 inch border all the way around the pastry, being careful not to cut all the way through the pastry. Using a fork, prick the center (inside the border) with small marks to keep the pastry from puffing up during baking.
In a small bowl, combine the ricotta, ¼ teaspoon salt, black pepper, red pepper flakes, and gralic powder. Spread the mixture on the interior (center) of the border, being careful to spread inside the marked lines. Lay the tomato slices over the ricotta so that tomatoes cover the rciotta but are not overlapping each other. Sprinkle with additional salt.
Bake pastry for 20-25 minutes, or until crust has puffed and is golden brown. Allow to cool for a few minutes.
While pastry is cooling slightly, toss together the arugula, olive oil, and a pinch of salt. Scatter the arugula over the top of the pastry. Cut into squares and serve immediately.