Preheat oven to 350 degrees F. Lightly oil a 9 x 13 baking dish or coat with nonstick spray.
Spread bread cubes in a single layer on a baking sheet. Place into oven and bake until crisp and golden, about 10-12 minutes; set aside.
Heat olive oil in a large skillet over medium heat. Add sausage and cook until browned, about 3-5 minutes, making sure to crumble the sausage as it cooks; set aside.
Melt butter in the skillet. Add garlic, onion and celery, and cook, stirring occasionally, until tender, about 4-5 minutes. Stir in apples, sage and thyme until fragrant, about 1 minute.
In a large bowl, combine bread, sausage, apple mixture, walnuts and parsley; season with salt and pepper, to taste. Stir in chicken stock until absorbed and well combined.*
Spread bread mixture into the prepared baking dish. Place into oven and bake until top is browned, about 45 minutes.
Serve immediately.
Notes
*A mixture of breads such as sourdough, multigrain, whole wheat or pumpernickel can be used, if desired. Or you can simply use 1 (16-ounce) loaf of your choice.*This can be made 1 day ahead. Let cool; cover and chill.