The globally widespread instant messaging (IM) mobile applications such as WhatsApp or Telegram were not originally educational tools, but they have become platforms for peer to peer assessment (P2P). The IM applications offer "chatbots" or "virtual assistant bots" that help students by providing them a multitude of services in the form of text or voice dialogs. A new method for integrating P2P assessment using voice recordings with the help of a chatbot is proposed. By using this system we can effectively improve both the typical learning and the P2P evaluation process of a massive open on-line course (MOOC). After a 2-month experiment, with 77 students that recorded 737 voice answers with a Telegram based chatbot, we describe in detail how to use a chatbot and the way to design voice-based challenges to perform a new kind of assignment in a MOOC, with 90% of the learners encouraging us to use chatbots in future courses.