Prepare grill for medium heat OR preheat oven to 450. In a large skillet cook the onion in oil over medium high heat until crisp tender, 4 to 5 minutes. Add mushrooms, cook until tender, 4 to 5 minutes. Stir in the tomato paste, basil and oregano. Cook until tomato paste startes to carmalize, 6 to 8 minutes. Stir in broth, stirring to loosen brown bits from bottom of pan. Bring to a boil. Cook untl sauce is thickened, 8 to 10 mintues. Remove from heat, cool slightly.