Preheat the oven to 350 degrees F.
Fry the bacon in a large skillet over medium-high heat until crispy.
Add the onions and cook until soft and translucent, about 4-5 minutes.
Add the mushrooms and garlic and cook for another 4-5 minutes until the mushrooms are soft.
Transfer the mixture to a bowl.
Melt the butter in the same skillet and whisk in the flour.
Once combined, continue whisking for another 2 minutes until the mixture has slightly deepened in color.
Add the half-and-half and chicken broth while constantly whisking to prevent lumps.
Once slightly thickened, add the cheese and whisk until melted and combined.
Next add the mushroom/bacon mixture along with the salt and pepper.
Let the sauce simmer for a couple of minutes, then add the green beans.
Stir to combine.
Pour the bean mixture into a 9x13 casserole dish and sprinkle the French fried onions all over the top.
Bake uncovered for 30 minutes until bubbling and the onions are golden and crispy.
Let sit for 5 minutes before serving.
