Heat the oil in a pot on medium-high heat. Add onions (chopped or blended) to the pot. Sauté for about 5 minutes. Add minced garlic to the onions and sauté them together for about 15-20 minutes. If the onions start to stick to the bottom of the pan, add a little bit of water to deglaze.
Once the onions are a deep golden-brown colour, add the cubed chicken breast and season with salt. Cook until no longer pink. Add the curry powder and mix. Cook for about 3 minutes.
Add tomato paste and mix. Cook until the bitter tang of the tomato paste is almost gone. Adding a little sugar at this point will help cut through the bitterness of the tomato paste. Add a little water if contents are sticking to the bottom of the pot.
Mix in the coconut milk. Turn the heat down to medium-low and let it simmer for a good 20-30 minutes. Stir every few minutes to make sure it's not sticking to the bottom of the pot. Cook the sauce until it gets to your desired thickness. The longer it cooks, the thicker it will become.