Combine 2 tbsps oil, chopped garlic, chopped green chillies, chopped onion, chopped spring onion greens, cinnamon powder, all-spice powder, black pepper powder, thyme sprigs, brown sugar, salt and chopped ginger in a bowl. Mix well and add soya sauce. Mix
Add chicken breasts in the bowl and rub the marinate on them nicely. Set aside for 15-20 minutes.
To make salsa, combine tomato, onion, green chillies, spring onion greens, tomato juice, salt, crushed peppercorns and lemon juice in a bowl. Mix well and set aside.
Heat oil in a non-stick grill pan. Place the marinated chicken breasts on it and grill for 2-3 minutes. Flip and grill for 2-3 minutes.
Shred lettuce leaves and slice onion. Mix them together. Add lemon juice and salt and mix well.
Place some of the lettuce-onion salad on a serving dish and spread to make a bed.
Remove grilled chicken from heat and slice them.
Place a little portion of lettuce-onion salad in each taco shell. Put some chicken slices, top with spoonful of salsa and a dollop of sour cream.
Place prepared taco shells on lettuce-onion salad bed and serve immediately.