Bring a large pot of heavily salted water to a rolling boil. Add the rotini pasta and cook according to package directions until al dente. Before draining, reserve about 1 cup (240ml) of the starchy pasta water. Drain the pasta and set it aside.

Pat the chicken breast chunks dry and season generously with salt and pepper. Heat olive oil in a large skillet over medium-high heat. Add the chicken in a single layer and sear for 3-4 minutes per side, until a deep golden-brown crust forms. Remove the chicken from the skillet and set aside.

Reduce heat to medium, add butter to the skillet. Once melted, add the diced onion, celery, and carrots and sauté for 5-7 minutes until softened. Add minced garlic and cook for 1 minute until fragrant. Sprinkle flour over the vegetables and whisk for 60 seconds.

Slowly pour in the chicken broth while whisking continuously. Then, slowly whisk in the heavy cream. Bring to a gentle simmer and cook for 5-8 minutes, until the sauce is thick and glossy.

Stir the seared chicken, cooked rotini, and frozen peas into the cream sauce. Stir gently until everything is coated. If the sauce is too thick, add a splash of reserved pasta water. Season to taste with salt and pepper. Serve immediately, garnished with fresh parsley and black pepper.