Preheat your oven to 375°F and lightly grease a 9x13-inch baking dish. This step helps the casserole cook evenly and prevents sticking later when serving the creamy green bean mixture.

Bring a large pot of salted water to a boil and cook the green beans for about 4 minutes. Drain them well and set aside so they stay bright and slightly crisp.

Heat olive oil in a large skillet over medium heat. Add diced onion and sliced mushrooms, then cook for 5 to 6 minutes until soft, golden, and full of flavor.

Add minced garlic to the skillet and cook for one minute until fragrant. Stir in flour and cook briefly, allowing it to form a light base that thickens your dairy free sauce.

Slowly pour in vegetable broth and almond milk while whisking constantly. Cook for 3 to 4 minutes until the sauce thickens slightly and becomes smooth and creamy without any lumps.

Season the sauce with salt, black pepper, and soy sauce. Stir well and taste, adjusting seasoning if needed so the sauce feels balanced, savory, and rich without using dairy ingredients.

Add the cooked green beans into the skillet and mix gently until everything is coated in the creamy sauce. The mixture should look glossy, well combined, and ready for baking.

Transfer the mixture into your prepared baking dish and spread it evenly. Sprinkle one cup of French fried onions over the top to create a flavorful and crispy layer.

Cover the dish with foil and bake for 20 minutes. This helps the casserole heat through completely while keeping the sauce creamy and preventing the topping from burning too early.

Remove the foil, add the remaining fried onions, and bake uncovered for another 10 to 15 minutes until the top is golden and crispy. Let it rest slightly before serving warm.