In a large bowl whisk together the yogurt, garlic paste, lemon zest, lemon juice, olive oil, sazon, paprika, coriander, cumin, oregano, mint, parsley and salt. Add the chicken thighs and toss together so the chicken is fully coated in the marinade. Let sit for at least 1 hour and up to overnight.
Preheat your oven to 375 F. Line a sheet tray with foil, then place the thick onion slice onto the tray. Stick two skewers into the onion so they are standing up straight. Skewer the chicken thighs onto the two skewers, layering them on top of eachother. Wrap the tops of the skewers with foil.
Place the chicken skewer into the oven and roast for 20-25 minutes, until the chicken is cooked through and slightly golden brown. Let rest for 5-10 minutes then slice the chicken into pieces off the skewer.
Return the cut chicken to the foil lined sheet tray to the oven on high broil for 3-5 minutes to crisp up the chicken. Remove from the oven and set aside until you assemble your gyro.
To assemble: Heat up your pita slightly in the oven, spread tzatziki over the middle of the pita then layer the french fries, chopped tomato, red onion and a heaping pile of chicken onto the pita. Wrap it all up and enjoy.
