Place the cooked chickpeas, egg whites, hemp seeds, cumin, garlic powder, sea salt, and black pepper in a food processor.
Pulse the mixture until a coarse, uniform paste forms, being careful not to over-process into a puree.
Finely chop the fresh parsley and stir it into the chickpea mixture by hand.
Divide the mixture into four equal portions and shape them into firm, round patties.
Heat the olive oil in a non-stick skillet over medium heat.
Place the patties in the skillet and sear for 4 to 5 minutes per side until they are golden-brown and crispy.
While the falafel cooks, whisk together the Greek yogurt, tahini, and lemon juice in a small bowl until smooth.
Serve the warm falafel patties immediately with the lemon-tahini sauce drizzled over the top.