Bring a large pot of salted water to a boil, then add the green beans and blanch for 3-4 minutes until bright green and slightly tender. Drain and set aside to cool.
In a large mixing bowl, whisk together the cream of mushroom soup, milk, minced garlic, smoked paprika, and half of the shredded cheese until smooth and creamy.
Gently fold the blanched green beans into the sauce, ensuring they are evenly coated. Taste and season with salt and pepper as needed.
Transfer the green bean mixture into your baking dish, spreading it out evenly with a spatula.
Sprinkle the remaining shredded cheese over the top, followed by a generous layer of crispy fried onions for that irresistible crunch.
Bake the casserole uncovered in a preheated oven at 180°C (350°F) for 25-30 minutes, until bubbling around the edges and the top is golden brown and crispy.
Remove the casserole from the oven and let it rest for 5 minutes to allow the sauce to set slightly. Serve hot, garnished with extra fried onions if desired.