Combine all chicken marinade ingredients in a large bowl. Whisk together well.
Place chicken in a large ziploc bag and pour marinade over chicken.
Let marinade for 2 hours up to overnight.
When ready to cook the chicken, prepare a cast iron pan or a grill. Preheat to get the skillet or grill hot on a medium heat, for at least 5 minutes.
Using tongs add chicken to pan and sear for 5-7 minutes on each side, until slightly charred.
Once cooked through, remove from heat and let rest for 5 minutes. Then chop into bite-sized pieces and set aside until ready to serve.
Before cooking the chicken, prepare the tatziki so it can chill in the fridge while you make the rest of the tacos.
To start, grate your cucumber on a cheese grater. Place the grated cucumber in several large paper towels and squeeze tightly over the sink to remove all the water. Try to get as much water out as you can.
Add the grated cucumber to a small bowl or tupper ware and then stir in remaining tatziki ingredients. Stir well until combined, then cover with aluminum foil or airtight lid and refrigerate until ready to eat.
Before cooking the chicken I also like to roast the veggies. Preheat your oven to 450 F degrees.
Add the sliced red onions and halved grape tomatoes to a large baking sheet. Lightly drizzle with olive oil and a sprinkle of salt. Toss gently with your hands.
Roast veggies at 450 for 5 minutes. Remove from oven and set aside.
After making the tatziki and roasted veggies, cook the chicken and cut it up.
Assemble tacos onto flatbread but adding a spoonful of tatziki, then topping with chicken, roasted veggies, diced cucmbers, feta, and some fresh herbs and lemon juice. Enjoy!