Step 1: Marinate the Chicken

1. In a bowl, add yogurt, chicken tikka masala, and lemon juice. Mix well to make a smooth marinade.
2. Add the chicken breast piece and coat it properly from all sides. Let it rest for at least 20 to 30 minutes. For deeper flavor, you can marinate it for 1 to 2 hours.

Step 2: Cook the Chicken

1. Heat a pan with a little oil. Place the marinated chicken in the pan and cook it like a steak on medium heat.
2. Cook both sides until the chicken is fully cooked, juicy, and slightly charred from the outside. Once done, remove it from the pan and let it rest for a few minutes.
3. After resting, shred the chicken using two forks or your hands.

Step 3: Prepare the Veggies

1. In a large bowl, add chopped capsicum, shredded carrot, chopped onion, mint leaves, and any other vegetables you like.
2. You can also add coriander, sweet corn, olives, jalapeños, or finely chopped cabbage if you want more texture.

Step 4: Make the Creamy Sauce

1. In a separate bowl, add mayonnaise, mustard sauce, salt, black pepper, and chili sauce.
2. Mix everything together until smooth. Taste and adjust according to your preference. Add more chili sauce for spice, more mayo for creaminess, or a little lemon juice for freshness.

Step 5: Mix the Filling

1. Add the shredded chicken to the bowl of veggies. Add shredded mozzarella cheese.
2. Pour the creamy sauce over the mixture and mix everything well until the chicken, veggies, and cheese are fully coated.
3. The filling should look creamy, colorful, and easy to spread.

Step 6: Assemble the Sandwich

1. Take two bread slices. Spread a little sauce on both inner sides of the bread.
2. Add a generous amount of the chicken and veggie filling. Place one cheddar cheese slice on top.
3. You can also add black olives, jalapeños, extra mozzarella, or chili flakes at this stage.
4. Cover with the second bread slice.

Step 7: Toast Until Golden

1. Heat a pan on low to medium heat. Add a little butter or oil.
2. Place the sandwich in the pan and cook until the bottom side turns golden brown and crispy. Flip carefully and toast the other side.
3. Press lightly with a spatula so the cheese melts inside and the sandwich becomes crisp from outside.
4. Once golden and melted, remove from the pan and cut in half.