Meanwhile, warm the oil in a large, heavy-bottomed pot over medium heat.
Add onion and cook, stirring occasionally until it's lightly browned in spots (~ 5 to 8 minutes).
Add tomato paste, remaining garlic, ginger, and spice mix. Cook, stirring frequently until the spices are fragrant and the tomato paste has started caramelizing on the bottom of the pot (~ 2 minutes)
To the pot, add the crushed tomatoes, along with the liquid in the can, the cream, water, and chopped cilantro. Season with salt and pepper and stir, scraping up any bits from the bottom of the pot.
Bring to a simmer and reduce the heat to medium-low. Cook, stirring occasionally until flavors meld and the sauce has thickened slightly (~30 to 35 minutes)
Remove from heat and cover until chicken is ready (or after cooling, refrigerate if marinating chicken for more than 4 hours).