If the chicken breasts are thicker than 2cm, then slice it in half lengthwise or butterflying them. This helps it cook faster and evenly. Then place the chicken in a medium bowl, add 1 tbsp olive oil, mild curry powder and 1/2 tsp salt. Mix well, ensuring the chicken is fully coated.
Bring a large saucepan to a medium-high heat. Add the remaining olive oil and butter. Place the chicken breasts in the pan, with any remaining oil and curry seasoning that's left in the bowl. Brown the chicken on one side for 3-5 minutes or until golden brown. Flip and cook for another 2-3 minutes. Remove from the pan and set aside.
In the same pan, reduce the heat to medium and add diced onions. Sauté until the onions turn golden brown and start to caramelize, approx. 5 minutes.
Meanwhile, bring a medium pot of salted water to a rolling boil. Once boiling, add the pasta, give it a quick stir to ensure it doesn't stick together and boil for 5 minutes, no longer. Once cooked, drain the pasta and set aside.
Add the tomato paste. Sauté until the tomato paste starts to darken approx. 1-2 minutes. Immediately add the tomatoes, garlic, curry paste and 1/3 cup water. Stir and simmer until the tomatoes start to soften, approx. 3-5 minutes.
Meanwhile, strip the cooked chicken breasts apart using your fingertips or two forks. Set aside.
Once the tomatoes have softened, add 1 cup cream and 1 tsp salt. Stir well. Followed by the torn chicken and any remain chicken liquids to the sauce. Stir again and add the drained pasta.
Allow the pasta to rest before serving. This allows the pasta to soak up some of the sauce and "marry" together. Salt to taste before serving and garnish with freshly chopped coriander or parsley.