In a small bowl, use a small spatula or a fork to combine the tomato paste, water, kosher salt, garam masala, curry powder, paprika, and crushed red peppers, to create a thick paste. Set aside.
Measure out the cream and remove it from the fridge to bring it to room temperature.
Heat the butter in a large, deep skillet over medium-high heat for about 2 minutes. Add the onion and cook, stirring often, for about 4 minutes, until soft.
Add the garlic, ginger, and seasoning paste. Cook for 1 more minute, stirring.
Add the chicken cubes. Stir to coat. Sauté the chicken on all sides for 2 minutes.
Add the canned tomato sauce. Keep cooking over medium-high heat, stirring, for 3-5 more minutes, until the chicken is cooked through.
Lower the heat to low and stir in the heavy cream to create a silky, creamy sauce. Serve immediately, garnished with parsley.
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Notes
While you want the chicken pieces to be cooked through, you don't want them overcooked and dry. So make sure to only cook them until they're cooked through (165°F internal temperature) and not longer.
Canned tomato sauce will give you a smooth and velvety sauce. You can also successfully use Pomi Chopped Tomatoes. Diced tomatoes (undrained) are another option that I tested and liked, but they do result in a chunkier sauce. If you opt to use them, chop them finely before using them.
You can keep the leftovers in the fridge, in an airtight container, for 3-4 days. To avoid drying the chicken, reheat them gently, covered, in the microwave at 50% power.