Step 1

Preheat oven to 350°F. Bring a large pot of salted water to a boil. Add the green beans and cook until crisp-tender, about 4 minutes; drain in a colander and let cold water run over the beans to cool and stop the cooking. Drain again and set aside.

Step 2

Heat the olive oil in a large skillet over medium-high. Add the mushrooms and cook, undisturbed, until golden on the bottom, about 5 minutes. Toss and continue to cook, stirring occasionally, until the mushrooms have released most of their liquid, 2 to 3 minutes more. Season with 1/2 tsp. salt and cook 30 seconds. Transfer mushrooms to the colander with the beans, reserving the skillet for the sauce.

Step 3

In a small bowl whisk the cornstarch and 2 Tbsp. of the vegetable broth to form a slurry; set aside. Combine the remaining broth, oat milk and soy sauce in the skillet and season generously with freshly ground black pepper. Bring to a simmer over medium heat. Stir the prepared slurry and add to the skillet, stirring to incorporate. Continue to cook, stirring, until mixture starts to bubble and is thick enough to coat the back of a spoon.

Step 4

Fold in the prepared green beans and mushrooms. Stir in 1/4 cup of the fried onions. Transfer the mixture to a 2-quart baking dish. Top with remaining fried onions and bake until bubbling and beginning to brown, about 15 minutes.