Boil a large pot of salted water and cook the penne pasta until al dente.
Drain the pasta while reserving one cup of the starchy pasta water for sauce adjustment.
Season the thin chicken breasts generously with salt and pepper.
Heat olive oil in a large skillet over medium-high heat.
Sear the chicken for five minutes per side until golden brown and cooked through, then remove from the skillet.
In the same skillet, add the minced garlic and sauté until fragrant.
Stir in the sun-dried tomatoes and heavy cream, bringing the mixture to a gentle simmer.
Whisk in the parmesan cheese until the sauce is smooth and thickened.
Add the baby spinach and cook until just wilted.
Return the chicken to the skillet, fold in the cooked pasta, and add reserved pasta water as needed to reach the desired consistency.