Heat oven to 375-degree Fahrenheit.
The first step involves cooking the green beans in a large bowl for about 3 to 5 minutes. The duration of cooking will entirely depend on how crispy you want the green beans to be.
Now, use a slotted spoon and transfer the beans into a bowl filled with ice water. Going forward, stir the beans to halt the cooking.
Then, transfer the onion in a separate plate and saute the Panko breadcrumbs in butter until it turns golden in color. Then, take a bowl and add onions, Panko, Parmesan, salt, and pepper and stir thoroughly.
While preparing Alfredo Sauce, briefly rinse and dry a saute pan. Now, pour butter on the pan and melt it over medium heat. Add mushrooms and saute for 5 minutes
Stir until it turns light brown and soft. Add garlic and saute it
Again, stir the contents and add the vegetable stock
Stir the contents thoroughly. Continue cooking until the mixture thickens. Next, remove the heat and season it with salt and pepper.
Mix the green beans and mushroom alfredo sauce and stir the mixture. Next, spread the green bean mixture in an even layer. Then, sprinkle the onion topping mixture uniformly.
Bake it for 25 minutes.
Finally, remove the bowl from the oven and serve warm.