Cook the pasta: Bring a large pot of salted water to a boil and cook the fettuccine according to the package directions until al dente. Reserve about 1 cup of the pasta water, then drain and set aside.

Season and sear the chicken: Toss the chicken strips with 1 1/2 tablespoons of the cajun seasoning until evenly coated. Heat the olive oil in a large skillet over medium-high heat and sear the chicken for 6-7 minutes, turning once, until browned with charred edges and cooked through to 165°F. Transfer to a plate.

Saute the jalapenos and garlic: Reduce the heat to medium and melt the butter in the same skillet. Add the jalapenos and cook for 2 minutes until softened, then stir in the garlic and cook for 30 seconds more.

Build the sauce: Pour in the chicken broth and scrape up any browned bits from the bottom of the pan. Stir in the heavy cream and the remaining 1/2 tablespoon cajun seasoning, and simmer for 2-3 minutes until slightly thickened.

Add the parmesan: Reduce the heat to low and stir in the parmesan and salt until the sauce is smooth and creamy.

Combine and finish: Return the chicken and any juices to the skillet along with the drained fettuccine. Toss to coat, loosening with a splash of the reserved pasta water if needed. Top with sliced green onions and serve warm.