Ready the falafel mix according to the box instructions (usually mix with water and let sit). Heat up oil in shallow pan. Using a small scoop of falafel, test the heat of the oil, flipping when golden-brown. Make small falafel patties and put them into the oil, flipping when crispy but not dark (use tongs, forks, or other utensils to flip the patties away from you, to avoid oil splatter). Assemble pitas with hummus and tahini.
Cut up onion, cucumber, and tomato.
To serve, spread hummus on a pita. Place falafel, onion, cucumber, and tomato on top and garnish with parsley. Add feta if desired.