Put red chilli sauce into a bowl, add soy sauce, ginger-garlic paste, lemon juice and sugar and mix well. Add a little salt and mix again.
Make criss-cross deep gashes on both the chicken breasts, apply the marinade well over them and set aside for 20 minutes to marinate.
To make tomato jam, heat 2 tbsps oil in a non-stick pan, add cumin seeds and onion seeds and saute till fragrant. Add garlic and saute. Add ginger and continue to saute till garlic browns.
Add tomatoes and mix and cook.
Heat 2 tbsps oil in a non-stick grill pan.
Add salt to the tomatoes and cook till tomatoes are pulpy. Add black pepper powder and sugar and mix well. Cook on low heat.
Put the chicken breasts in the grill pan and grill. When the underside is done, turn them over and cook the other side similarly.
Add vinegar to the tomato jam and mix well. Add the remaining marinade to the tomato jam and mix well.