Fill a large pot with water and bring it to a boil. Add a pinch of salt and the trimmed green beans. Blanch them for about 3-4 minutes until they turn bright green and are crisp-tender. Immediately transfer the beans to a bowl of ice water to stop the cooking process and preserve their vibrant color. Drain well and set aside.
Heat 1 tablespoon olive oil in a large skillet over medium heat. Add the diced onion and cook until translucent, about 4-5 minutes. Add the sliced mushrooms and cook until they release their moisture and become soft, about 6-7 minutes. Stir often for even cooking.
Pour in 2 cups of chicken broth and bring to a simmer. Stir in the garlic powder, onion powder, salt, and pepper. Slowly add 1 cup of heavy cream, stirring constantly to prevent curdling. Let the sauce simmer gently until it thickens slightly, about 5-7 minutes.
Add the blanched green beans and chopped turkey bacon to the skillet with the creamy mushroom sauce. Stir well to coat everything evenly. Taste and adjust seasoning if necessary.
Preheat your oven to 350°F (175°C). Transfer the green bean mixture into your casserole dish, spreading it out evenly. Sprinkle the crispy fried onion pieces generously over the top to create a crunchy crust.
Place the casserole in the preheated oven and bake uncovered for 20-25 minutes until the topping is golden and the sauce is bubbling around the edges. Remove from the oven and let it rest for a few minutes before serving.
