When I type the command in adb:
./adb shell am start -W -a android.intent.action.VIEW -d \"example:gizmos\" com.myapp
I get this error:
You don't need to specify full path to your activity, but if you want to test whether you react properly to URI in your app just specify app package:
adb shell am start -a android.intent.action.VIEW -d "example://gizmos" com.myapp
Also there is bug in command you provided - there should be example://gizmos
not example:gizmos