Boil salted water and cook 8 oz spaghetti according to package directions. Reserve 1/4 cup pasta water before draining.
Season 1 lb chicken breasts evenly with 1 tsp salt, 1/2 tsp black pepper, 1 tsp paprika, and 1 tsp garlic powder.
Heat 1 tbsp olive oil in a large skillet over medium-high heat. Sear the seasoned breasts for 5 to 7 minutes per side until the internal temperature reaches 165°F. Remove from the skillet, let rest, and slice.
In the same skillet, melt 4 tbsp unsalted butter over medium heat. Add 4 minced garlic cloves and 1/4 tsp red pepper flakes; sauté for 1 minute until fragrant.
Stir in the reserved 1/4 cup pasta water and simmer for 1 to 2 minutes to slightly thicken. Toss in the drained spaghetti, sliced chicken, 1/2 cup grated Parmesan cheese, and 2 tbsp chopped fresh parsley. Serve immediately.