Add the ground chicken, minced red onion, garlic, lemon juice, oregano, salt, and black pepper to a large mixing bowl.
Mix well with your hands to combine.
Spoon the ground chicken mixture onto each tortilla, spreading it into a smooth, flat, even layer.
Add the olive oil to a large frying pan over a medium heat.
Add a tortilla to the pan, chicken-side down, and cook for 4–5 minutes, until browned.
Flip the tortilla over and cook on the other side for another 2 minutes. Repeat with the remaining tortillas. Use two pans to speed things up, if desired.
Spoon the tzatziki onto each tortilla.
Scatter over the diced cucumber, tomato, red onion, and chopped parsley to serve.
