Cook the pasta: Bring a large pot of salted water to a boil. Cook the pasta until just shy of al dente. Reserve 1/2 cup of pasta water, then drain.

Season the chicken: Pat the sliced chicken dry. Toss with 1–1.5 tablespoons Cajun seasoning, a pinch of salt, and pepper.

Sear the chicken: Heat olive oil in a large skillet over medium-high. Add chicken in a single layer. Sear 3–4 minutes per side until browned and cooked through. Transfer to a plate and tent loosely with foil.

Sweat the aromatics: Lower heat to medium. Add butter. Stir in onion and peppers with a pinch of salt. Cook 4–6 minutes until softened and lightly caramelized. Add garlic and cook 30 seconds until fragrant.

Bloom the spices: Sprinkle in the remaining Cajun seasoning and stir 20–30 seconds. If using, add tomato paste and cook 1 minute to concentrate flavor.

Build the sauce: Pour in chicken broth and simmer 2–3 minutes, scraping up browned bits. Stir in heavy cream and bring to a gentle simmer.

Temper the yogurt: In a small bowl, whisk Greek yogurt with a few spoonfuls of hot sauce from the pan until smooth. Stir the tempered yogurt into the skillet to prevent curdling.

Add cheese and adjust: Stir in Parmesan until melted. If the sauce is too thick, loosen with a splash of pasta water. Taste and adjust salt, pepper, and Cajun seasoning.

Combine: Add the drained pasta and cooked chicken (plus any juices) to the skillet. Toss until the pasta is well coated and everything is hot.

Finish: Squeeze in a little lemon juice to brighten. Garnish with chopped parsley or green onions. Serve immediately.