Chicken Shawarma

Name: Chicken Shawarma
Ingredients: 1 tablespoon ground coriander; 1 tablespoon ground cumin; 1 tablespoon ground cardamom; 1 tablespoon chili powder; 1 teaspoon smoked paprika; 1 tablespoon grill seasoning, recommended brand Montreal; 1 lemon, Juice of, divided; 2 large garlic cloves, grated, finely chopped; 5 tablespoons extra-virgin olive oil, divided; 4 chicken breasts, boneless, skinless (about 6 to 8 ounces each); 1 large onion, sliced; 1 red bell pepper, sliced; 1 yellow bell pepper, sliced; 1⁄4 cup tahini; 1 1⁄2 cups Greek yogurt; 4 pita bread