The process was relatively relaxed. I was approached by the companies internal recruiter over LinkedIn and decided to have an initial call. It was short, lasting around 30 minutes and served as an initial interview/vetting call of sorts (non-technical). Essentially, if you can hold a conversation and give a good idea of your experience and what you are looking for with the company, you will likely be forwarded onto the second phase.
After this, a call was scheduled with the Technical Director. Very approachable person and extremely friendly. He gave a good overview of the company from a consultants perspective and provided the merits for working at Zerodaylab. Some general technical questions were asked, more to get a feel for your experience and what areas you are knowledgable in. This may be different for junior consultants but my impression was that having a track record of employment in other security companies and demonstrable experience, the second call is more a "feeler" call to understand what areas you are strong in and which of those you are lacking.
Finally, I found out I was successful after being approached by the initial internal recruitment manager who gave some feedback and arranged a final call with the technical director to finalise any details before a formal offer was issued.
Overall a pleasant experience, and great to be able to speak to the technical director who you will work closely with if you are successful.