Preheat the oven to 350 degrees F. Grease a 9X13 casserole dish and keep it aside.
Meanwhile, bring a large pot of salted water to boil, blanch the green beans for 3-5 minutes and transfer them to an ice bath to stop the cooking process. Set aside.
Heat a heavy bottom pan with butter on a medium flame. Once the butter has melted add the onions and minced garlic, saute till the onions turn translucent.
Sprinkle the flour and stir for a minute and add in the milk and chicken broth. Cook for 2-3 minutes until the sauce thickens.
Add the spices; paprika, pepper, and salt. Remove the pan from the heat and add the cheddar and parmesan cheese. Stir constantly, the cheese will melt in the heat, and then add half a portion of the fried onions into the sauce mixture.
Stir in the blanched green beans without the water and fold them into the sauce mixture.
Transfer the green beans along with the cheesy sauce into the prepared casserole dish. Bake for 20 -25 minutes until warm and bubbly around the edges.
Add in some more french fried onion on top and serve.