Preheat the oven to 375°. In a medium bowl, use your fingers to rub the horseradish, lemon zest, celery salt and cayenne pepper into the sugar. Add the tomatoes and Worcestershire and toss to coat.
Lightly grease a rimmed baking sheet with grapeseed oil and place the tomatoes, cut-side up, in the pan. Season with salt and pepper. Roast until the tomatoes are tender and shriveled, about 1 hour, and 15 minutes. Cool to room temperature and serve immediately or refrigerate for up to 5 days.