Green Bean Casserole I

From Trader Joe's.

1-1/2 Tbsp. butter
1-1/2 Tbsp. olive oil
1 bag Trader Joe’s Sliced Cremini Portabella Mushrooms
1/4 sweet onion, sliced
1 bag (24 oz.) Trader Joe's Frozen French Green Beans
1 container Trader Joe’s Cream of Portabella Mushroom Soup
1/2 C. water
1-1/2 C. Swiss cheese, shredded
1/2 can Trader Joe’s Gourmet Fried Onion Pieces

Preheat oven to 375 degrees. Heat olive oil and butter in a large heavy skillet; add mushrooms and sauté until they become soft and lightly browned. Add onion and continue to sauté until soft and lightly browned. Add green beans and sauté until heated through. Add soup and water to skillet, mix and heat through. Add mixture to a small or medium size casserole. Top with cheese. Top cheese with fried onion pieces; place in the oven and bake until cheese melts and becomes warm and bubbly, about 15 to 20 minutes.

Notes: When I make this again, I want to double the mushrooms which may require more soup. I'm also curious about substituting cream/milk for water.