Preheat oven to 425 degrees F. Lightly grease a baking sheet and set aside.
Divide pizza dough into 4 pieces. Lightly dust work surface with flour. Roll out each piece into an 8-inch circle.
Arrange tomatoes, olives, rosemary, arugula, tuna and cheese over half of each dough circle. Brush entire edge of dough with water. Fold dough nearly in half to cover filling, leaving an inch of the bottom half sticking out. Fold lower piece over top piece and pinch to seal. Poke 2 small holes in the top to let steam escape.
Transfer to prepared baking sheet and bake until golden brown, about 12 minutes.
Remove from heat and let cool a few minutes before serving.