In a large bowl, whisk together 3 tablespoons of olive oil, 2 tablespoons of lemon juice, 3 minced garlic cloves, and 1 tablespoon of dried oregano to create the marinade.
Add the 1.5 lbs of boneless, skinless chicken thighs to the bowl, tossing to coat thoroughly. Cover and refrigerate for at least 30 minutes.
Preheat the grill to medium-high heat. Grill the marinated thighs for 6 to 8 minutes per side, or until the internal temperature reaches 165°F.
Remove the meat from the grill and let it rest for 5 minutes before slicing it into thin strips.
Warm the 4 pita breads on the grill for about 30 seconds per side.
Assemble the wraps by spreading 1/4 cup of tzatziki sauce on each warm pita. Top with sliced meat, 1/4 cup shredded lettuce, 1/8 cup sliced red onion, 1/4 cup sliced cucumber, and 1/4 cup halved cherry tomatoes.