In a large pot, heat the vegetable oil over medium heat.
Add the finely chopped onion and sauté until golden brown, about 5-7 minutes.
Add the minced garlic and grated ginger, and cook for another minute until fragrant.
Stir in the chopped tomatoes and bell pepper.
Cook for about 5 minutes until the vegetables start to soften.
Stir in the tomato paste, ground cumin, ground coriander, ground turmeric, ground black pepper, and salt.
Cook for another 2-3 minutes to allow the spices to bloom and the mixture to thicken slightly.
Pour in the water or fish broth and bring the mixture to a boil.
Reduce the heat to low and let it simmer for about 10 minutes to allow the flavors to meld together.
Gently add the fish chunks to the pot.
Simmer for another 10-15 minutes, or until the fish is cooked through and flakes easily with a fork.
Stir in the lemon juice and adjust the seasoning with more salt and pepper if needed.
Garnish the kajaik with fresh chopped cilantro or parsley.
Enjoy your meal!