Preheat the oven to 350 degrees F (175 degrees C).
Season the skinless side of the turkey breast with 1/2 of the kosher salt and herbes de Provence. Season the skin side with the remaining kosher salt. Place turkey skin-side up into an oiled baking dish.
Roast in the preheated oven until an instant-read thermometer inserted into the turkey registers 148 degrees F (64 degrees C), 45 to 60 minutes.
Place bacon on a baking sheet lined with aluminum foil. Remove turkey from the oven and let cool.
Bake bacon in the hot oven until about halfway cooked, 10 to 15 minutes.
Melt butter in a pot over medium heat. Stir in flour until combined. Cook, stirring occasionally, until roux smells like cooked pie crust, about 3 minutes. Whisk in cream all at once. Cook until Mornay sauce is thickened and starting to boil, about 5 minutes. Immediately turn off the heat.
Season Mornay sauce with salt, black pepper, and cayenne pepper. Stir in 1/2 cup Pecorino Romano cheese until combined. Add nutmeg and stir briefly.
Cut turkey into thick slices. Pull off the skin.
Stack 2 bread slices on top of each other and trim off the crusts. Cut 1 slice into 2 triangles. Place bread in a small baking dish set on top of a sheet pan. Top bread with 3 slices of turkey. Place 3 tomato slices in between. Ladle 1/4 of the Mornay sauce all over and cover with 2 tablespoons Pecorino Romano cheese. Sprinkle with paprika; lay the partially cooked bacon across the top. Repeat with remaining ingredients to make 3 more servings.
Set an oven rack about 6 inches from the heat source and preheat the oven's broiler.
Bake under the broiler until bacon is crispy and the tops are well browned, about 5 minutes. Place on napkin-lined plates and sprinkle parsley over each dish.
Feel free to buy thick-cut deli turkey so you don't have to make the turkey yourself.
Substitute Parmesan cheese or a nice extra-sharp Cheddar for the Pecorino Romano if desired. Substitute cayenne for the paprika if preferred.
Instead of broiling, you can finish by baking in the oven at 475 degrees F (246 degrees C) for the same results. To cheat, you can cook bacon crisp separately, and just top the finished dish, but I think it tastes better if you brown with the bacon on top.
Per Serving: 1280 calories;85.4 g fat;
36.6 g carbohydrates;
88.7 g protein;
400 mg cholesterol;
2841 mg sodium.