Soak fenugreek seeds 6 hours or more. The seeds will swell to be about 3 times in volume. Drain the water.
In a pressure cooker add 1-1/2 cups of water and all the ingredients except sugar cook over medium high heat. After cooker start steaming lower the heat to medium and let it cook for about 8-10 minutes.
Open the pressure cooker after steamed has escaped, mix it well mash the mango slices.
Add the sugar, mix it well and let it simmer for 2-3 minutes. Chutney should have consistency of thick gravy, if needed add little more water.
Methi chutney can be served warm or at room temperature.