Heat the oil in a skillet on medium heat for 2 minutes. Add the onions to the hot oil and sauté for 2 minutes. Stir in the garlic and ginger, if using, and sauté 2 or 3 minutes more.
Stir in the tomatoes, chili pepper, and salt. Stir in tomato paste and water or stock.
Simmer about 15 minutes on medium-low heat, or until the gravy