Preheat oven to broil. Spray an 8x8-inch baking dish with nonstick cooking spray. Set aside.
In a medium saucepan, melt butter over medium heat. Add flour, whisking to combine. Cook 1 minute, stirring constantly. Gradually add milk, whisking until smooth. Cook, whisking constantly, until thickened, approximately 6 minutes. Stir in 1⁄2 cup Swiss, Cheddar, salt, and pepper until smooth. Remove from heat. Set aside.
Place bread in an even layer in prepared dish, trimming as needed to fit. Layer turkey evenly over bread; top with cheese mixture. Sprinkle with remaining 1⁄2 cup Swiss and paprika.
Broil until cheese melts and begins to brown, approximately 4 minutes. Top with bacon, tomatoes, and parsley, if desired.
Recipe by Taste of the South at https://tasteofthesouthmagazine.com/kentucky-hot-brown-casserole/