Which of the following would require a teaspoon for service?

The correct answer is chocolate lava cake, which is served with a spoon because it typically has a molten center. A teaspoon is needed to scoop up the cake and enjoy the rich, flowing chocolate within. This dessert is often served warm, and the gooey interior enhances the dining experience, making a spoon the most appropriate utensil for this dish.

In contrast, chocolate mousse, while also a dessert, is usually served in a small cup or bowl, where a dessert spoon or even a fork may be more appropriate for its light and airy texture. Peppercorn steak is a savory entrée that would be served with a knife and fork, as it requires cutting and managing larger pieces of meat. Grilled vegetables, similar to the steak, would typically be handled with a fork and possibly a knife, depending on the size of the pieces. Thus, the nature of the chocolate lava cake distinctly necessitates a teaspoon for effective enjoyment, setting it apart from the other options.