Place the diced bagels on a baking sheet and bake for 8 minutes, or until it is dried out and lightly browned.
Heat 1/4 cup vegetable broth in a large skillet over medium. Saute onions, celery, garlic, bell pepper and mushrooms, and cook on medium until everything is soft and translucent.
In a large mixing bowl, combine the bagel cubes, the cooked ingredients, and all the remaining ingredients except the broth and toss together. Once uniform, pour the broth in slowly while gently mixing to moisten the ingredients evenly.
Transfer the mixture to a baking dish and bake for 35 to 40 minutes, or until the bagel chunks are lightly browned.