Heat the oven to 375 degrees F.
Drizzle the tilapia pieces with olive oil and lemon. Sprinkle with salt and pepper.
Bake the tilapia for about 12 minutes, or until the fish is cooked through.
Pick the parsley leaves from their stems. Wash the parsley. Finely chop the parsley, and set aside.
Thinly slice the onions and tomatoes. Set aside.
In a medium sized pan, heat a few tablespoons of oil. Add the sliced onions. Sprinkle with salt. Cook on low to medium heat, until the onions are nearly caramelized. Add more oil as needed, if the onions start to stick to the pan.
When the onions are nearly caramelized, add the curry and cayenne powders. Stir for a few minutes. Add the vinegar, and stir. The onions should now be tender, with a rich yellow color.
Add the tomatoes to the onions. Sprinkle some salt. Cook on medium heat until the tomato slices have dissolved.
Add the chopped parsley. Stir into the onion and tomato mixture. Turn off the heat.
Spoon the tomato onion topping, or khulta, onto the fish. Serve by itself, or alongside rice or bulgur.