Fill a 6-quart / 5.7 L pot with 3 L of water, add the salt and bring to a boil. While it heats, pat the chicken dry, cut it into 2 cm / 3/4-inch pieces and toss with 1 tbsp of the Cajun seasoning. Dice the onion and bell pepper and mince the garlic.

Add the cottage cheese, milk, Parmesan and the remaining 1 tbsp Cajun seasoning to a blender. Blend for 45 to 60 seconds, scraping down once, until completely smooth with no visible curds.

Heat 1 tbsp olive oil in a 30 cm / 12-inch deep skillet over medium-high heat. Add half the chicken in a single layer and sear for 5 to 6 minutes, turning once or twice, until browned and 165 F / 74 C in the center of the largest piece. Move it to a plate.

Drop the penne into the boiling water and set a timer for 1 minute less than the package time, about 9 minutes. Add the remaining 1 tbsp oil to the skillet and sear the second batch of chicken for 5 to 6 minutes until browned and 165 F / 74 C. Move it to the plate.

Lower the heat to medium. Add the onion and bell pepper to the same skillet and cook for 3 to 4 minutes, scraping up the browned bits, until softened. Stir in the garlic and tomato paste and cook for 1 minute until fragrant and brick red.

Scoop out 240 ml of pasta water, then drain the penne. Reduce the skillet heat to medium-low and pour in the blended sauce. Stir for 2 minutes until it's warm and steaming gently, not bubbling. Add the pasta, the chicken with its juices and 120 ml of the pasta water, and toss for 2 minutes until the sauce coats everything. Loosen with more pasta water a tablespoon at a time if it's tight, taste for salt, and top with green onions.