1In a medium saucepan, combine the diced mango, chopped onion, grated ginger, minced garlic, mustard seeds, chili flakes, ground cumin, and salt.
Add the brown sugar and apple cider vinegar to the saucepan and stir well to combine all ingredients.
Place the saucepan over medium heat and bring the mixture to a gentle boil, stirring occasionally.
Reduce the heat to low and simmer uncovered for 40-50 minutes, stirring occasionally, until the chutney thickens and the mango becomes soft and jammy.
Taste and adjust seasoning if needed. Remove from heat and let the chutney cool slightly.
Transfer the chutney to sterilized jars and allow it to cool completely before sealing.
Store in the refrigerator for up to 2 weeks. Serve as a condiment with curries, grilled meats, or cheese platters.