Comment 5 for bug 1357072

I was also following https://elementary.io/docs/code/getting-started#bazaar and had the same problem. What's happening is that the compiler needs a folder where it can find the Vala files it needs. The message says:

By not providing "FindVala.cmake" in CMAKE_MODULE_PATH this project has
  asked CMake to find a package configuration file provided by "Vala", but
  CMake did not find one.

The "FindVala.cmake" file was in cmake-modules/src (in my case, you'd need to find out how that works for you), so I opened up my CMakeLists.txt in my app's root folder and added this to it's fourth line:

list (APPEND CMAKE_MODULE_PATH ${CMAKE_SOURCE_DIR}/cmake-modules/src)

After that I could configure and build everything.