Preheat oven to 375 degrees F. Spray an 8x8-inch baking dish with non-stick cooking spray.

Set a large skillet over medium heat and add the butter. When butter is melted, crumble in the plant-based sausage, using a spatula to break up any large chunks.

Add celery and onion. Cook, stirring frequently, for 5 minutes, until sausage is browned and vegetables are softened.

Add stuffing mix and water. Gently stir to combine with the sausage mixture and ensure all the stuffing mix is damp. Remove from heat.

Pour the stuffing mixture into the prepared baking dish. Bake for 20 minutes, until the stuffing is golden brown. Serve hot.