Preheat the oven to 400 degrees F.
Lay the bacon out on parchment lined, rimmed baking sheet and sprinkle each slice with a thin, even layer of brown sugar. Bake until the bacon is beginning to brown and crisp, but is not completely done, about 8 to 10 minutes. It will continue to cook with the hot browns. Remove from oven and set aside.
Toast the bread in a toaster, until lightly browned. Cut each piece of toast diagonally into triangles and overlap 3 triangles into each of 4 individual oval-shaped baking dishes. Alternatively, hot browns can be assembled and baked on ovenproof dinner plates.
Mornay Sauce: In a medium saucepan over medium heat, add the butter and cook until the bubbling begins to diminish, indicating that the water in the butter is evaporating. Add the flour and stir with a wooden spoon to form a roux, cooking and stirring constantly for 2 to 3 minutes, being careful not to let the roux brown. Add the milk all at once, and continue to stir with a wooden spoon or whisk, while bringing mixture to a simmer.
Continue to cook until smooth and thick, using a whisk to break up any lumps that form. Turn off the heat and add the Cheddar and Swiss cheeses, stirring until melted and combined. The cheese will thicken the sauce, so additional milk may be added, if desired. Season with salt and pepper, to taste.
Cover the toast in each baking dish with about 1/4 cup of sauce. Then top with a layer of roasted turkey. Cover the turkey with additional sauce and put 2 strips of the bacon on top in a crisscross fashion. Sprinkle each dish with about 1 tablespoon of grated Parmesan and bake until bubbly, about 10 minutes.
While the hot browns are baking, combine all the ingredients for dressed tomatoes in a medium-size bowl and toss to combine.
During the last 2 to 3 minutes of baking, turn on the broiler to brown the tops of the hot browns. Remove from oven and serve hot, with a small dish of tomatoes on the side or piled atop the hot browns, if desired.
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