Interactive software development can follow different kinds of processes, from specification-driven approaches (traditional methods) to prototype-driven approaches (agile methods). Due to the emphasis in documentation since its initial phases, traditional methods allow for more reflection on the software before its implementation and contribute to better maintainability. On the other hand, agile methods have reduced documentation, concentrating mainly on the implementation of the system, in order to increase the productivity in the software development process. As software becomes more interactive and accessible to a wider range of users, human-computer interaction (HCI) concerns have been gaining emphasis in the software development process. However, schedule and budget restrictions limit the application of known and accepted HCI techniques. As a consequence, and similar to what happened with software development processes, there has been a tendency to adopt simplified usability practices, such as checklists and guidelines. In order to deal with such concerns at design time, and in a way that is not so simplified, this work unites some advantages of different kinds of software development processes to define an HCI design process. This process brings together the support for reflection given by the Semiotic Engineering (SemEng) theory and the agility of interface prototype techniques, incorporating the values and practices from agile methods, more specifically of the eXtreme Programming (XP) development process.