Preheat oven to 375°F.
Combine ground flax with water and refrigerate for 10 minutes to allow the mixture to thicken.
In a pan heated to medium, sauté mushroom and onion in olive oil for 3 to 4 minutes. Add garlic and cook for another 1 to 2 minutes.
Add the mushroom and onion mixture to a food processor along with rinsed and drained chickpeas, the thickened flax and water mixture, and remaining falafel ingredients. Process until everything is well combined and the mixture comes together as a thick batter.
Take approximately 1 ½ tablespoons of the mixture and form balls. Place on a parchment lined baking sheet. Bake for 30 minutes, flipping the falafels half way through.
While the falafels are baking, prepare hemp tabbouleh and maple tahini sauce.
For the tabbouleh, finely chop parsley leaves and add to a bowl along with remaining ingredients and stir to combine.
For the maple tahini sauce, place all the ingredients in a high-powered blender and combine until smooth.
Warm up the mini pitas in the oven during the last couple minutes of baking the falafels.
To assemble the falafel sliders, cut mini pitas in half and spread maple tahini sauce on the inside of the bottom half. Place hemp tabbouleh on top, add a falafel, and dollop with more maple tahini sauce. Serve immediately.