Beans - Add the beans to a medium size saute pan, try to get them mostly in a single layer if possible and cover with water. Just enough to cover. Bring to medium heat and cook 4-5 minutes until crisp, but slightly tender - no need to cover. You don't want them all the way cooked, but tender. Once they are done. Drain and remove to a casserole dish sprayed with a non stick spray.
Bacon (or pancetta) - In that same pan, pour out any water and add the oil to the pan and bring to medium heat. Add the diced bacon or pancetta and 30saute until golden brown. About 5 minutes stirring often, you want it crisp. Remove to a plate lined with a paper towel to drain and then transfer to the casserole dish with the beans.
Onions/Mushrooms - Using some of the drippings from the bacon (about 1 teaspoon) add the onions and mushrooms and saute until, once again, slightly tender, but not over done. Medium heat. Season with salt and pepper. Remove and add to the casserole dish with the beans and bacon.
Mushroom Broth - Again, t that same pan, add the butter and bring to medium heat until melted. Then stir in the flour and whisk well until combined, cook just a minute until the flour taste is gone. Add in the broth and bring to a medium boil. The sauce will naturally thicken. Add in the soy sauce, cream, salt and pepper to taste, cook just another minute and it is done. Pour the sauce over the vegetables and mix well to combine.
Bake Casserole - To the green bean casserole, stir in 2/3 cup of the french fried onions and bake at 350 for 20-25 minutes until bubbly, uncovered. After 20-25 minutes, remove and gently stir, then top with the remaining french fried onions around the edge of the casserole and sprinkle the cheese in the center. Bake another 5 minutes until the onions are golden brown and the cheese is melted.