Final answer:
In the sentence provided, the verbal 'to own an ice cream truck' functions as a noun, acting as a subject complement after the linking verb 'is'.
Step-by-step explanation:
In the sentence "My dream is to own an ice cream truck," the function of the verbal "to own an ice cream truck" is used as a noun. It serves as the subject complement following the linking verb 'is,' which is a form of the verb 'to be.' The subject complement in this case renames the subject 'My dream' and specifies what that dream entails, hence functioning nominally rather than adverbially.