Special equipment: a 3 1/2 to 4-inch diameter round cookie cutter
In a large bowl, combine the chicken, mozzarella, spinach, mascarpone, Parmesan, tomato-basil sauce, basil, lemon juice, salt and pepper.
Position an oven rack in the center of the oven and preheat to 425 degrees F. Spray a standard 12-cup muffin pan with nonstick spray.
Lightly flour a work surface. Roll out the pizza dough to a thin large round, about 1/8-inch thick. Using a 3 1/2- to 4-inch-diameter round cutter, cut out 12 rounds for pizza crusts. Working with 1 crust at a time, settle 1 dough round into the prepared muffin pan. Press and pull the dough up the sides of the cup. Rotate the pan and repeat until the dough covers the bottom and sides. Pack in 2 to 3 tablespoons of filling. Repeat with the remaining dough rounds and filling.
Bake the pizzas until the crusts are golden brown and the filling is bubbling, 16 to 18 minutes. Let stand 1 minute. Then use a small knife to loosen the pizzas. Arrange on a platter and serve.