For the chicken: combine yogurt, lemon juice, garlic cloves, olive oil, vinegar, true life sea salt, thyme and whisk it until it is all combined. Add the chicken tenders and red onions, stir up the contents so everything is covered with the marinade. Let marinate for 15 min (or you can do this and let marinate overnight).
Preheat oven to 400 degrees. Line a baking sheet with aluminum foil and then place a wire cooling wrack on top of the aluminum foil. Take the chicken and red onions out of the marinade and place on the rack. Bake for 10 minutes, flip and bake for another 10 minutes.
While the chicken is baking prep the cucumbers by slicing the cumbers and then adding the vinegar and spices and set aside.
To assemble put one - two chicken tenders in the pita, a few pieces of cucumber slices, a few leaves of spinach and a spoonful of feta cheese and enjoy!