Stuffed Pasta Shells

1 20-oz. package of cheese-stuffed pasta shells
8-oz. mushrooms, sliced
2 tsp olive oil
1 28-oz. can plum tomtoes, cut up
1 6-oz. can low-sodium tomato paste
1/2 tsp dried oregano
1/2 tsp garlic powder
1/2 cup white wine

Saute the mushrooms in the oil in a skillet for about 5 minutes. Transfer them to the stoneware. Add the tomatoes, tomato paste, oregano, garlic and wine. Cover and cook on High for 3 1/2 to 5 hours. Add the shells to the sauce, making certain to cover them with sauce. Cover and cook for about 1 hour or until the shells are thoroughly hot.