Step 1: Preheat oven to 400°F (200°C). Arrange Texas toast slices on a baking sheet. Bake for 5-7 minutes, or until lightly golden and toasted. Set aside.
Step 2: In a large skillet, cook bacon slices over medium heat until crispy. Drain on paper towels and set aside. Once cooled, you can break them into smaller pieces if desired.
Step 3: In a medium saucepan, melt butter over medium heat. Whisk in the flour and cook for 1-2 minutes, stirring constantly, until a smooth paste (roux) forms and smells slightly nutty.
Step 4: Gradually whisk in the milk, a little at a time, ensuring no lumps form. Continue whisking until the sauce thickens to a creamy consistency, about 5-7 minutes. Bring to a gentle simmer, stirring frequently.
Step 5: Remove the saucepan from the heat. Stir in the grated Gruyère cheese and 1/4 cup Parmesan cheese until melted and smooth. Season with nutmeg, salt, and black pepper to taste. Keep the sauce warm.
Step 6: For each serving, place two slices of toasted Texas toast side-by-side in an oven-safe dish or on a baking sheet. Arrange half of the sliced turkey over the toast.
Step 7: Generously spoon about half of the warm Mornay sauce over the turkey and toast.
Step 8: Top each with half of the cooked bacon slices and two tomato wedges. Sprinkle with additional Parmesan cheese.
Step 9: Place the dish in the preheated oven and bake for 10-15 minutes, or until the sauce is bubbly and the edges are golden brown. For extra browning, you can broil for the last 1-2 minutes, watching carefully to prevent burning.
Step 10: Remove from oven. Garnish with fresh parsley. Serve immediately.