Place the chopped tomatoes, chillies and into a large bowl. Mix well and leave in the fridge overnight to macerate.
The following day, place a saucer in the fridge to get cold. This will be used to test whether the jam is ready after cooking.
Add all the spices (excluding the ginger and garlic) to a spice bag using a muslin cloth. Tie up the bag and secure it tightly so that the spices don't get into the jam but release their flavours during cooking.
Transfer the tomato and chilli mix from the fridge to a heavy based pan, along with the ginger and garlic, salt, lemon juice and vinegar, and the spice bag.
Bring the mixture to a boil. then turn the heat down to a simmer. Stir regularly to ensure the mixture doesn't burn as it thickens. After 30 minutes test the jam to see if it has thickened enough. To do this, remove the saucer from the fridge and place a teaspoon of jam on it. Let it set for a few minutes and run your finger through the jam. This should leave a clean finger mark on the saucer where the jam has separated. If it is still too runny, cook the mixture for a little longer and repeat the process with the saucer.
Once you are happy with the consistency, let the jam cool and transfer it to jars and store it in the fridge. This recipe makes quite a large quantity so it's perfect for sharing with friends.