01 - Bring a large pot of generously salted water to a rolling boil. Add the cheese tortellini and cook according to package directions until al dente. Drain well and set aside.
02 - Pat the diced chicken breasts dry and season evenly with salt, pepper, and Italian seasoning. Heat olive oil in a large skillet over medium-high heat until shimmering. Add the seasoned chicken in a single layer and cook undisturbed for 2 minutes, then continue cooking and turning until golden brown and cooked through, 5 to 7 minutes total. Transfer to a plate and tent loosely with foil.
03 - Reduce the heat to medium and melt the butter in the same skillet. Add the chopped onion and sauté for 2 to 3 minutes until softened and translucent. Stir in the minced garlic and cook for 1 minute until fragrant, being careful not to let it brown.
04 - Pour in the chicken broth and use a wooden spoon to scrape up any browned bits from the bottom of the skillet. Let the liquid simmer for about 1 minute to reduce slightly.
05 - Pour in the heavy cream and add the grated Parmesan cheese. Stir continuously over medium heat until the cheese has fully melted and the sauce begins to thicken, approximately 3 minutes. Avoid boiling to prevent the sauce from breaking.
06 - Add the fresh baby spinach to the sauce and gently stir until just wilted, about 1 to 2 minutes.
07 - Return the seared chicken to the skillet along with the drained tortellini. Gently toss everything together until evenly coated in the creamy garlic sauce. Taste and adjust seasoning with additional salt and pepper as needed.
08 - Serve immediately in warmed bowls, garnished with extra Parmesan and freshly chopped parsley if desired. Pair with a crisp Pinot Grigio for a complete dining experience.