Peel and dice the eggplant, about 1/2-inch dice. In a large saute pan, over medium heat, add the oil. When the oil is hot, add the onions. Season with salt. Saute for 2 minutes. Add the eggplant. Season with salt. Continue to saute until soft, about 15 minutes. Add the curry powder and lemon juice. Continue to saute for about 2 minutes. Remove from the heat and serve Mango Chutney with grilled fish or chicken.
Place all of the ingredients, except for the turmeric and ground red pepper in a saute pan, over medium heat. Cook until dark toasted, about 12 minutes. Remove and cool. Place the toasted ingredients in a spice grinder and process to powder consistency. Add the turmeric and red pepper. Mix well.
In a saucepan, over medium heat, melt the butter. Add the onions. Season with salt. Saute for 2 minutes. Add the mango. Continue to saute for 2 minutes. Add the vinegar and sugar. Bring the mixture to a boil. Whisk the cornstarch with the water. Whisk until smooth. Stir the slurry into mango mixture. Bring the mixture back to a boil. Continue to cook for 4 minutes, stirring constantly. Remove from heat and cool completely. Store in an airtight container until ready to use.