This uses a jarred cooking sauce, which I don’t often use. But the sheer quantity of spices and seasonings used in Indian cooking can make the jarred pastes and sauces a reasonable choice, unless you really plan to cook a lot of Indian dishes.
You can add other vegetables. The original called for cauliflower, more red pepper and fresh tomatoes. I just used what I had in the kitchen. If you use something that cooks quickly, like spinach or peas, add them at the end. The Jalfrezi curry is shown to the right in the picture here. To the left is chicken biryani curry.