Make tandoori chicken. Put the chicken breasts into a bowl with 4 tablespoons yogurt, ketchup, curry powder, chili powder, ginger and 2 teaspoons grated garlic. Add salt and black pepper to taste. Rub the chicken breasts, cover and refrigerate for 1 hour.
Make cilantro chutney. Put cilantro, chopped onion, minced garlic, 1/2 teaspoon salt, 1 teaspoon sugar, 1/8 teaspoon cayenne pepper and lemon juice into a food processor. Process to a fine paste.
After 1 hour, take the chickens out. In a skillet, heat olive oil over medium heat. Put chicken breasts into the skillet and cook until the bottom sides are brown. Turn the chickens, cover, reduce heat to medium-low heat and cook chickens until chickens are no longer pink.
Wipe off the fat in the skillet and add butter and the marinade sauce remaining in the bowl. Simmer for about 2-3 minutes until the sauce is thickened shaking the skillet to coat the chickens with the butter and sauce. Remove the skillet from the heat and let cool.
Make Raita sauce. In a small bowl, mix together 4 tablespoons yogurt, 1/4 teaspoon sugar, ground cumin, 1/16 teaspoon cayenne pepper and 1/16 teaspoon salt.
When the chickens have cooled, slice each chicken breast into 6.
Assemble sandwiches. On 1 slice bread, put lettuce leaves, put raita sauce, 2 tomato slices, 3 cucumber slices, 3 slices tandoori chicken and spread cilantro chutney on top. Put the other slice bread to close sandwich. Repeat this to make 3 more sandwiches.