For the coconut spice paste:
If using an electric pressure cooker, heat it to its brown or sauté setting (whichever is hotter). If using a stovetop pressure cooker, place the uncovered pot over medium heat. Roast the red chilies and shallots together until all have developed black spots. Remove and set aside in the bowl of a small food processor.
Add the coconut and whole spices to the hot pressure cooker pan and cook for about 1 minute, stirring constantly until fragrant and toasted and the coconut has turned light brown. Add the turmeric and stir for another few seconds, then transfer coconut and spices to the food processor bowl.
Blend until fairly smooth, adding a 4 to 6 tablespoons of water to create a creamy paste. Set aside.
For the chicken curry:
Add oil to the hot pressure cooker pot. When hot, add chopped ginger, garlic, and sliced onions. Sauté for 10 to 15 minutes, or until onions are softened and browned around the edges. Add the coconut spice paste and fry for 1 minute. Add the sliced tomatoes and fry for 5 more minutes or until tomatoes have broken down. Stir in the chicken, salt, and vinegar. Mix well.
Cover the pressure cooker and lock the lid. Bring up to pressure. Cook on HIGH pressure for 10 minutes, then let the pressure release naturally (this will take another 8 to 15 minutes).
The chicken should be thoroughly cooked, but if it is not, or if it is not as tender as you would like it to be, pressure cook for another 4 minutes, using the quick pressure release to immediately let out the steam after the cook time.
Serve with basmati rice and yogurt.