Preheat oven to 350°. Spray a 2½-quart baking dish with nonstick cooking spray.
In a large bowl, place bread. Pour 1½ cups water over bread, and let stand 15 minutes.
Spray a medium skillet with cooking spray. Add onion, bell pepper, celery, and garlic. Cook over medium heat until tender, stirring often, about 5 minutes. Remove from heat, and set aside. Cool slightly.
Add 1 cup cheese to bread mixture, stirring to combine. Add onion mixture, water chestnuts, and crabmeat, stirring gently to combine.
In a medium bowl, whisk together egg and egg whites. Add mayonnaise, salt, pepper, and hot sauce. Add egg mixture to crabmeat mixture, stirring gently to combine. Spread into prepared pan. Sprinkle top with remaining 1 cup cheese. Bake until filling is set, bread is toasted, and cheese is melted, 35 to 40 minutes.
Recipe by Louisiana Cookin' at https://louisianacookin.com/crabmeat-egg-casserole/