Over high heat, add 1 tablespoon oil to the same heavy-bottomed pan or Dutch oven used to cook the aromatics. Once hot, add the chicken in a single layer and cook for 2-3 minutes on each side, or until brown and just starting to char. Remove chicken to a clean plate and set aside (do not worry if the chicken is not fully cooked on the inside).
Scrape out any charred bits stuck to the bottom of the pan and repeat process until all chicken has been cooked (it took me 2 rounds).
Wipe down the pot, or clean as needed, and return to medium high heat.
Add 1 tablespoon of oil to the pan and add the onions. Cook for 1-2 minutes, stirring frequently. Add the bell peppers, salt, water (or broth), 4-6 tablespoons of the prepared curry paste, and the reserved cinnamon sticks and cardamom pods. Thoroughly mix to combine and cook, stirring often, for 2-3 minutes.
Stir in the coconut milk and mix thoroughly. Increase heat to high and bring to a simmer.
Immediately reduce heat to medium and return the browned chicken to the pot. Add the sugar and fish sauce, mixing well to combine. Allow chicken and vegetables to simmer for 2-3 minutes, uncovered.
Season with additional salt, sugar, curry paste, or fish sauce, to taste. Serve with cooked basmati rice, jasmine rice, or noodles or thick, fluffy naan bread, if desired.