Preheat the oven to 350°F. Spray a 9x13-inch baking dish with cooking spray. Set aside.

In a large pot, bring 3-4 quarts of salted water to a boil. While the water is coming to a boil, trim the ends of the green beans and cut them into segments about 1-2 inches long.

To prepare the mushrooms, clean by wiping off excess dirt with a damp cloth. Trim the stems, then either dice them or cut them into slices about the thickness of a quarter. Set aside.

When the water is boiling, add the green beans and cook for 3-4 minutes. Drain and immediately run the green beans under cold water to stop the cooking process.

In a large, high-sided saute pan or dutch oven, heat the butter and olive oil over medium heat. Add the mushrooms and onion, along with a pinch of salt. Cook down until most of the liquid has cooked out of the mushrooms and they are beginning to caramelize.

Add the garlic; cook for 1 more minute. Sprinkle the flour over the mixture and stir to coat the vegetables; cook for 1-2 minutes.

Slowly add the stock, lemon juice, 1 teaspoon of the soy sauce, and a pinch of salt and pepper. Bring to a simmer, stirring constantly. Taste, adding additional soy sauce, lemon juice, or salt and pepper if desired.

Remove from the heat and add the cream of mushroom soup, parmesan cheese, and the blanched green beans, stirring to combine.

Pour the mixture into the prepared baking dish. Top evenly with the fried onions. Bake for 20-25 minutes or until the edges are bubbling and the topping is golden.