Preheat oven to 350 degreesIn a small bowl, mix together the crumbled crackers and french fried onions. Add in the melted butter and set aside.Melt 1 tablespoon of butter in large skillet and add in your garlic. Cook for 1 minute and then add in the mushrooms and onion. Once sauteed, season with salt and pepper, remove from pan and set aside.In the same skillet, add in 2 tablespoons of butter and when melted, whisk in flour. Cook for 1 minute and then stir in sour cream, Greek yogurt, salt.Mixture will be lumpy, so slowly start to add in your milk, whisking to combine. You may need or desire a little more milk to make it a thick liquid but I stopped at ¼ cup.Add back in your mushroom and onion mixture and your green beans.Stir to combine and then add in ½ cup cheese.Pour into 2½ quart casserole dish and sprinkle with remaining cheese and top with fried onion/cracker mixture.Bake for 30 minutes until top is nice and golden brown.