Preheat oven to 350 degrees F.
Boil fresh green beans in a saucepan for approximitly 5 minutes on medium - high heat. Or follow instructions on green beans package. If using canned green beans, just drain and set aside.
In a cast iron skillet or use any skillet, fry bacon until crispy. Once it's done, remove bacon and cool on plate with a paper towel. Once it is cooled break bacon into little pieces.
In the same skillet used for bacon, remove the majority of the grease leaving just a little. Add fresh sliced mushtooms and cook for 3 minutes.
Add the minced garlic to the pan with the mushrooms and cook for an additional 2 minutes.
In a large bowl mix together the green beans, cream of mushroom soup, half and half, crumbled bacon, mushrooms, salt, pepper and 2 cups of fried onions.
Lightly grease a 2.5 quart casserole dish.
Pour the green bean mixture into a casserole dish.
Cook at 350 degrees for 25- 30 minutes or until mixture is hot and bubbling.
Add remaining fried onions (1/2 cup) on top of casserole and cook for an additional 5 minutes.