How to Make It
Preheat the oven to 275°. Line a baking sheet with foil and lightly oil the foil. In a small saucepan, combine the orange zest with the water and sugar and bring to a boil. Simmer over moderate heat until syrupy, about 10 minutes. Drain the zest. Spread the strips out on the baking sheet and bake for about 45 minutes, or until dry but not browned. Let cool completely, then grind to a powder in a spice grinder.
In a medium saucepan, melt the butter. Add the shallots and cook over moderately low heat until softened, about 4 minutes. Add the diced tomatoes and season with salt and pepper. Cover and cook over moderately low heat until the the tomato mixture is thick, 10 minutes.
Preheat the broiler. Spread the tomato mixture in a small, shallow baking dish. Layer the tomato slices on top, overlapping them slightly. Season with salt and pepper.
Toss the Parmesan with 1/2 teaspoon of the orange-zest powder and sprinkle over the tomatoes. Broil for 2 minutes, or until golden and bubbling. Serve hot.