Trim the ends off the bitter melons and slice them crosswise into rounds approximately 0. 25 inch / 6mm thick.
Place the slices in a bowl, sprinkle liberally with salt, place a weight on top, and set aside for at least 30 minutes to draw out the bitterness.
Rinse the slices thoroughly under running water, drain well, and pat completely dry with paper towels to ensure crispness.
Heat the oil in a 7–9 inch frying pan over moderate heat. If using mustard oil, allow it to reach the smoking point first to mellow its pungency.
Add the bitter melon rounds to the hot oil and stir-fry for 10–15 minutes, cooking on both sides until they are crisp and reddish-brown.
Remove the pan from the heat immediately.
Add the turmeric, paprika or cayenne, grated coconut, lemon juice, and the remaining 0. 25 tsp (125 ml) of salt.
Toss the mixture well to coat the chips evenly and serve hot or at room temperature.
Dryness is Key for Crunch: Pat the rinsed bitter melon slices completely dry. Any remaining moisture will cause them to steam instead of fry, resulting in soggy chips.
Don't Burn the Spices: Remove the pan from the heat *before* adding the coconut and spices. The residual heat is plenty to toast them without scorching them and turning them acrid.