Why do you need a tech spec? If founders need to choose between drawing boxes and writing code, the latter always wins.
If you see your team discussing a lot about potential solutions instead of coding. If you don’t see any real progress, chances are they need to write a tech spec.
One thing is to have detailed requirements, mockups, and acceptance tests; a completely different thing is to know “how” to implement them.
Tech Specs don’t need to be extensive technical documents. They need three ingredients: 1) a data model, 2) an architecture diagram, and 3) significant tasks.
Once your team knows exactly which data is required and how to store it; what would be the process to collect/store the data, and a simple breakdown of tasks, they will know exactly what to do to move forward.