Preheat oven to 350℉ degrees.
Clean and cut the ends off the green beans, then cut into bite sized pieces.
Bring a large pot of water to a boil. Carefully add the green beans to the water and allow them to cook for 5-7 minutes to desired softness. Keep in mind they will soften slightly more when baked.
Remove the green beans from the pot and place in a bowl of ice water to stop the cooking. Drain and set aside to let the beans dry off while preparing the sauce.
In a large skillet melt the butter over medium heat. Add the mushrooms and cook until softened. Add the garlic and cook an additional 30 seconds.
Sprinkle with flour and stir to create a thick paste. Cook for 2-3 minutes.
Whisk in the broth, half and half, salt and pepper and Worcestershire sauce. Bring to a simmer and let simmer for several minutes, as it cooks the sauce will thicken.
Remove sauce from heat and add in the parmesan cheese. Stir while the cheese melts into the sauce.
Add the green beans to the mushroom sauce, stir to coat. Add in 1/2 cup of the fried onions and stir.
Pour the green bean mixture into a baking dish.
Bake at 350℉ for 20 minutes. Sprinkle the remaining fried onions on the top and continue to back for an additional 5 minutes until golden brown.
Serve warm and enjoy.