Eclipse C/C++ (CDT) import files into project - header file not found - include path

I am trying to import files into an Eclipse C project and compile it. The build process cannot find the local header files. The header files are located in the src directory. How can I edit the include path in eclipse? If I were doing it manually I could specify the -I option in gcc.

Building file: ../src/averaging.c
Invoking: GCC C Compiler
gcc -O0 -g3 -Wall -c -fmessage-length=0 -MMD -MP -MF"src/averaging.d" -MT"src/averaging.d" -o"src/averaging.o""../src/averaging.c"
../src/averaging.c:2:23: fatal error: averaging.h: No such file or directory
compilation terminated.
make: *** [src/averaging.o] Error 1