Saute onion, mushrooms, and olives in butter.
Stir in flour, garlic powder, salt, and mushroom liquid; heat.
Prepare pastry according to package directions.
Roll out; cut into 2 1/2-inch circles.
Place 2 teaspoons tuna mixture in center of each pastry circle.
Fold pastry over.
Dampen edges; seal.
Bake in 450°F oven 7 minutes or until crust is golden brown.