Boil a large pot of salted water and cook the short pasta according to package instructions, approximately 8-10 minutes. Reserve 1/2 cup of pasta water before draining.

Season the sliced chicken breasts with garlic powder, salt, and pepper. Cook in olive oil and butter over medium-high heat for 5-7 minutes on each side until golden brown and internal temperature reaches 165°F. Transfer to a plate and rest before slicing.

In the same skillet, reduce heat and add butter. Add flour and whisk for 1 minute, then gradually stir in chicken broth and heavy cream. Mix to create a smooth sauce. Add pesto and lemon juice, simmer until slightly thickened, about 3-5 minutes.

Add fresh baby spinach to the sauce, stir, and cook for about 2 minutes until wilted.

Toss the drained pasta into the skillet with the sauce, adding reserved pasta water if needed to achieve desired consistency. Mix thoroughly to coat pasta.

Slice the rested chicken and arrange on top of the pasta. Garnish with Parmesan cheese if desired and serve immediately.