Heat 4 tbsp (60 ml) of peanut or vegetable oil in a nonstick wok or large frying pan over moderately high heat.
When the oil is hot but not smoking, drop in the 8–10 oz (230–285 g) of eggplant cubes and stir-fry until they are reddish-brown and crisp on the outside.
Remove the eggplant with a slotted spoon, drain on paper towels, and immediately sprinkle with 0. 5 tsp (2 ml) garam masala and 0. 5 tsp (2 ml) turmeric, tossing to coat.
Add the 2 tbsp (30 ml) of mustard oil (or remaining vegetable oil) to the same pan and heat until the mustard oil reaches the smoking point for a few seconds.
After a few seconds of sizzling, add the 16 oz (455 g) of spinach, 1 tsp (5 ml) jaggery, and 0. 5 tbsp (7 ml) salt.
Reduce the heat to moderate and cook for approximately 4 minutes, stirring frequently until the greens are wilted but still vibrant.
Fold in the 1 tbsp (15 ml) lemon juice and the spiced eggplant cubes, tossing gently just to reheat the eggplant without losing its crispness.