One option is to run ashSimpl.exe directly from avast! Antivirus installation folder.
Second option is like this:
Right-click on "a" ball next to the clock and select program Settings...
Under common section uncheck the "Test memory during application start-up".
With this option disabled avast! will open Simple Interface without splash screen.
But this will also couse avast! NOT to scan resident memory (RAM) before launching it's components. This is not good in case if some malware is still resident in memory.