Coat the bottom of a dutch oven or stock pot with a lid with olive oil and heat the oil over medium heat.
Add the cubed chicken thighs (unseasoned) to the hot oil and brown on all sides. When the chicken is browned on all sides, remove it from the pot and set it aside.
Add the onions to the pot and saute for about 5-7 minutes, until softened.
Add the peppers to the pot and saute for another 5 minutes, until just softened.
Add the spices (the Garam Masala through the cayenne) and stir to coat the veggies in the spices. Cook for 2 minutes, until the spices are fragrant.
Add the tomato paste and stir until its no longer in one big lump.
Add the tomatoes and their juice to the pot. Break the tomatoes up woth the bottom of your spatula or spoon.
Return the chicken to the pot and stir to combine everything. Reduce the heat to low, cover the pot, and simmer for one hour.
Meanwhile, prepare your rice according to package instructions.
Before serving the curry, add the cream, if desired. Serve immediately, piping hot, over rice.