In a small bowl, whisk together the sesame paste, yogurt, lemon juice and garlic until smooth. Fold in the cucumbers and season. Spread the 'tzatziki' on the pita and lay warm lamb and tomato slices on top. Spread more 'tzatziki' on the tomatoes and garnish with sesame seeds.
Plating: Slice in half and serve.
Beverage: Chilly lager or pale ale