I've been using this recipe all winter with green beans from the freezer - tastes great with both fresh or frozen green beans!
Source: adapted from allrecipes.com
2 1/2 lbs. fresh green beans, trimmed
2 c. sliced fresh mushrooms
2 T. onion, finely chopped
2 cloves garlic, minced
4 t. butter
1/2 t. salt
1/4 t. pepper
Steam green beans until crisp-tender. Meanwhile, in a large skillet, saute mushrooms, onion and garlic in butter until tender. Drain beans; add to skillet. Stir in salt and pepper; heat through.