In skillet, cook the beef, onion, green pepper and garlic over medium heat till done. Drain and set aside. In saucepan, bring tomato sauce and Italian seasoning to boil. Reduce heat and cover and simmer for 10 minutes. Stir 1/2 c. sauce into meat mixture.
Unroll pizza crust on floured surface. Roll into a 12inch square and cut into 4 equal squares. Spread cream cheese over each to within 1/2 in. of edges. Top with meat mixture. Sprinkle with mozzarella cheese, mushrooms and olives. Fold dough over filling forming a triangle; press edges with a fork to seal.
Place on greased baking sheet. Bake at 400 degrees for 20-25 minutes or until golden brown. Serve with remaining sauce.