Boil a large, salted pot of water for the pasta. Cook al dente according to package directions.
Meanwhile, cut the chicken lengthwise so you've got 4 thinner pieces. Season them with the garlic powder and salt & pepper.
Heat the oil and butter in a skillet over medium-high heat. Once the pan is hot, add the chicken and cook for 5-6 minutes/side or until it's cooked through. Transfer chicken to a plate. Let it rest for a few minutes and then slice it into bite-size pieces.
Sprinkle the flour into the skillet and cook for about 1 minute (there should still be some butter/oil in there, but if the pan is dry, add 1 tablespoon butter first).
Add in the chicken broth, cream, pesto, lemon juice, and sun-dried tomatoes to the pan. Scrape up any brown bits from the bottom. Let it gently simmer for a few minutes until it's thickened up a bit.
Stir in the spinach and let it wilt. Add in the drained pasta (add some of the hot pasta water prior to draining it if the sauce appears a bit thick) and toss.
Season with extra salt & pepper if needed, and serve with the sliced chicken on top and extra parmesan cheese if desired.