In a large pot, bring 4 liters of water and 2 tablespoons of salt to a rolling boil. Add penne and cook for 10-12 minutes until al dente. Reserve 120ml of starchy pasta water, then drain the pasta.

Pat the chicken cubes dry with paper towels and season with salt and black pepper.

Heat 2 tablespoons of olive oil in a large deep skillet over medium-high heat. Add chicken in a single layer and sear for 6-8 minutes, turning occasionally, until golden brown and the internal temperature reaches 74°C (165°F). Transfer chicken to a plate and set aside.

Reduce heat to medium. Add the remaining 1 tablespoon of olive oil to the same skillet. Add minced garlic and chili flakes. Sáute for 60-90 seconds until the garlic is golden but not browned.

Pour in the crushed tomatoes and add the sugar. Stir to deglaze the pan. Simmer uncovered for 12-15 minutes on medium-low heat until the sauce has thickened and reduced by approximately 20%.

Add the cooked chicken and any accumulated juices back into the skillet. Fold in the cooked penne and the reserved pasta water. Increase heat to medium-high and toss for 2 minutes to emulsify the sauce.

Remove from heat. Stir in the chopped parsley. Serve immediately in warmed bowls, topped with grated Parmesan cheese.