1. Combine the evaporated milk and flour in a jar with a tight-fitting lid, and shake until smooth. Set aside.
2. Tear the bread slice into small pieces. Place in a food processor or blender, and process into crumbs. Measure the crumbs. You should have 1/2 cup. (Adjust the amount if necessary.) Set aside.
3. Place the celery and 1 tablespoon of water in a large nonstick skillet. Cook and stir over medium-high heat for about 2 minutes, or until the celery is crisp-tender. Add the chicken broth, and bring the mixture to a boil. Shake the flour mixture, and slowly add it to the celery mixture, stirring constantly. Continue to cook and stir for another minute or 2, or until the mixture is thickened and bubbly. Stir in the water chestnuts, the mushrooms, and, if desired, the almonds.
4. Coat a 2-quart casserole dish with nonstick cooking spray, and place the vegetable mixture in the dish. Combine the bread crumbs and Parmesan cheese in a small bowl, and sprinkle over the mixture.
5. Bake at 350°F for about 35 minutes, or until the mixture is bubbly around the edges and the top is golden brown.