Mix all ingredients together with a mixer.
Place all ingredients in a food processor and blend until smooth. Add more garbanzo bean liquid and process if you want it thinner.
To assemble: Spread tzatziki sauce in the bottom of a shallow serving dish or pie plate. Spread hummus on top. Top with cucumber, tomatoes, onions, feta, and parsley.
Refrigerate for 2 hours to let the flavors meld before serving. Serve with pita chips.
Source: my friend Karin