Bring a large pot of salted water to a rolling boil. Add pasta and cook according to package instructions until al dente, usually 8-10 minutes. Reserve ½ cup of pasta water, drain and set aside.

Season chicken breasts with garlic powder, salt, and pepper. Heat olive oil and butter in a skillet over medium-high heat. Cook chicken for 5-6 minutes per side until golden brown and reaches 165°F. Remove and let rest.

In the same skillet, add flour to the remaining oil and butter. Cook for about 1 minute. Then add chicken broth, stirring to combine. Mix in heavy cream, pesto, and lemon juice until blended.

Allow the sauce to simmer for 3-5 minutes until slightly thickened. Fold in sun-dried tomatoes and spinach, cooking until spinach wilts.

Add drained pasta to the skillet and toss with sauce, using reserved pasta water to adjust consistency. Mix in sliced chicken and heat for 1 more minute. Serve garnished with Parmesan if desired.