Heat oil over medium heat in a large nonstick skillet. Add eggplant and fry gently for about 10 minutes. At first the oil is completely absorbed, but then is gradually released as the eggplant becomes fairly firm. Stir in chile peppers and garlic and cook for 3 minutes.
Stir in vinegar, chili powder, fenugreek, coriander, mustard, turmeric and salt. Bring to a boil, reduce heat and boil gently for about 10 minutes. Add sugar and cook for 2 minutes.
Remove hot jars from the canner and ladle relish into jars to within 1/2 inch of rim. Process 15 minutes for half-pint jars and 20 minutes for pint jars.