Preheat oven to 350 degrees
In a skillet over medium high heat, cook bacon until crispy. Set aside and chop when cooled.
Wipe some of the grease from skillet, but leave about 1 Tbs in the pan to fry your mushroom mixture. Cook mushrooms, onion, and garlic and set aside.
Steam frozen green beans until you have reached your desired tenderness.
Melt butter in skillet. Once butter is completely melted, add in your flour and whisk together. Once it starts to thicken (about 30-60 seconds), slowly add in half & half in increments until mixture is thickened.
Add in salt and pepper, italian seasoning, and 1 cup of parmesan cheese. Stir together until the cheese is melted. Add in chopped bacon, onion and mushroom mixture, and ½ cup of fried onions.
Top with ½ cup parmesan cheese and bake in oven for 20 minutes.
After 20 minutes, take your casserole out of the oven and top with 2 cups (or more!) fried onions until completely covered.
Put dish back into oven for 10 more minutes, or until casserole is bubbling.