Preheat the oven to 350 degrees F. Spray an 8X8 inch baking dish with cooking spray. Coat the chicken breast with lemon juice and oregano on both sides. Put the chicken breast in the baking dish and bake for about 25 minutes.
Once the chicken is done baking, place on a cutting board and slice into 1/2 inch strips.
Place the tortillas on a flat surface and smear the yogurt evenly on top. Divide the chicken, onion, cucumber, cheese, and mint evenly onto the tortillas.