Place the eggplant in a large colander, sprinkle with the salt and toss to combine. Place the colander in the sink and stand for 1 hour for the eggplant to degorge. Rinse the eggplant well and pat dry with paper towel.
Combine the eggplant, capsicum, onions, dates, vinegar, brown sugar, chillies, garlic and cumin seeds in a large heavy-based saucepan (about 4-litre/16-cup capacity). Stir over high heat until the sugar dissolves. Bring to the boil.
Reduce heat to medium-low and boil gently, stirring occasionally, for 1 1/2 hours or until all the excess liquid has evaporated and the mixture is thick. Stir the chutney more frequently towards the end of cooking.
Remove the saucepan from the heat and stand for 2-3 minutes. Stir and then ladle into hot sterilised jars. Seal tightly and turn upside down for 2 minutes. Invert and allow to cool. Label, date and store in a cool dark place for at least 1 month before using.
Serve with aged cheddar on crusty bread, with Indian curries, on roast beef sandwiches, with roast vegetables or pork, or add a spoonful to chunky vegetable soups.
This chutney will store in a cool, dark place for 6 months. Once opened, keep in the fridge for up to 8 weeks.