Preheat the oven to 400 degrees. Line a baking sheet with parchment paper and set aside.
In a small bowl, whisk together the flaxseeds and water. Set aside to thicken.
Add the onion, cilantro, parsley, and garlic into a food processor. Process until finely chopped. Add in the remaining ingredients, including the flax mixture, and process until the batter comes together and everything is incorporated.
Scoop half of the batter onto one end of the baking dish. Shape it into a circle and smooth out the top so that it is an even 1/4 inch thick. Repeat with the remaining batter on the other side of the baking sheet. Bake for 30 minutes.
Remove from the oven and let cool for 5 minutes. To each pizza, spread on a layer of hummus, then top with onions, cucumber, tomatoes, olives and parsley. Serve.