Cook the pasta according to the package instructions. Reserve 1/2 cup of pasta water before draining.
Season the chicken with salt, black pepper, garlic powder, and paprika on both sides.
Heat a drizzle of oil in a large skillet over medium heat. Cook the chicken for 4–6 minutes per side, or until fully cooked through. Remove from the pan and set aside. Cut the chicken into pieces.
Add a little more oil to the same pan if needed. Add the onion and sauté until softened and translucent.
Stir in the garlic and cook for 30 seconds, until fragrant.
Add the grape tomatoes and cook until they begin to burst and soften, about 4–5 minutes.
Stir in the tomato paste and cook for 1 minute to deepen the flavor.
Pour in the heavy cream and reserved pasta water. Stir until smooth and combined.
Season with chili flakes to taste.
Add the Parmesan cheese and stir until melted into the sauce.
Add the spinach and cook until wilted.
Slice or dice the cooked chicken and return it to the pan. Stir to combine.
Add the cooked pasta and toss until evenly coated in the creamy tomato sauce.
Serve immediately with additional Parmesan cheese and chili flakes, if desired.