Preheat oven to 400 degrees. In a medium bowl combine, breadcrumbs, garlic, lemon zest, Parmesan cheese, and parsley; set stuffing aside.
In a medium bowl, combine radicchio and oil. Season with salt and pepper; toss to combine. Arrange cut side down on a baking sheet. Bake for 10 minutes.
Remove from oven. Turn cut side up, and press stuffing into the crevices of the radicchio. Return to oven, and bake until tender when pierced with the tip of a knife, about 10 minutes more.
Remove from oven, and transfer to a platter. Drizzle with vinaigrette. Serve hot, warm, or at room temperature.