How to Make It
In a medium bowl, combine yogurt, ¼ cup tahini, olive oil, lemon juice, salt and pepper. Add chicken and mix to combine well.
Divide chicken mixture evenly between two slices of bread. Top chicken mixture with even parts onion, tomato, and spinach. Spread the remaining 2 teaspoons tahini evenly over the remaining 2 slices of bread; close each sandwich with bread slices, tahini side down. Serve immediately or wrap in plastic and refrigerate until ready to serve, up to 2 days.