Preheat oven to 375 degrees F (190 degrees C). Spray the insides of 4 ramekins.
Heat a large skillet over medium-high heat. Cook and stir sausage in the hot skillet until browned and crumbly, 5 to 10 minutes; drain and discard grease. Add onion, green bell pepper, and mushrooms; cook and stir until vegetables are softened, 2 to 3 minutes. Pour in pizza sauce and simmer until flavors have blended, 5 to 10 minutes. Stir 1/4 cup mozzarella cheese into sausage mixture.
Spoon 1/4 the sausage mixture into each prepared ramekin; top each with 1/4 the remaining mozzarella cheese.
Roll out the crescent roll dough; cut the dough into 4 equal pieces. Cover each ramekin with 1/4 the crescent roll dough, wrapping the dough around the edges to seal in the fillings. Arrange the pot pies on a baking sheet.
Bake in the preheated oven until dough is light golden brown, 10 to 12 minutes. Allow to cool for 10 minutes before serving.