Place all the ingredients in a high-speed blender and process until semi-smooth. Transfer it to a bowl.
To temper the spices, add the oil to a small pan on medium-low heat. When the oil is slightly warm, add the mustard seeds and curry leaves. Cook for 30 seconds. The seeds will sputter and the curry leaves will get crispy. (Keep the flame medium-low to prevent burning and too much sputtering).
Makes about 1 cup
Note: For an oil free version, skip tempering the spices in oil. Dry fry them over medium-low heat until the seeds begin to pop. The chutney is still very flavorful.