Season the chicken breast with salt, pepper, and a pinch of oregano. Cook in a skillet over medium heat for 5 to 7 minutes per side, or until fully cooked. Let it rest, then slice thinly.
While the chicken cooks, chop the lettuce, dice the cucumber, halve the cherry tomatoes, and thinly slice the red onion.
In a small bowl, whisk together olive oil, fresh lemon juice, oregano, salt, and black pepper to make the dressing.
Lay each tortilla flat. If needed, warm for 10 seconds to make it more flexible.
Layer lettuce first, then cucumber, tomatoes, onion, olives, and sliced chicken.
Sprinkle feta cheese evenly over the top.
Drizzle lightly with the prepared dressing. Do not overfill.
Fold in the sides of the tortilla and roll tightly from the bottom up.
Slice in half and serve immediately.