Bring pot of salted water to a boil and cook pasta for 10-12 minutes, or until al dente. Once cooked, drain and set aside.
In a deep sauté pan or skillet over medium heat, add 2 Tbsp olive oil and spinach. Season with salt. (You may do this in batches until all spinach is cooked if your skillet is not large enough.) Add diced chicken and cook until spinach is wilted and chicken is warmed through. Remove to a plate and set aside.
In sauté pan, add 1 Tbsp olive oil. Add minced onion and cook until soft, about 2 minutes. Add minced garlic, sun dried tomatoes, and oregano, and cook for another minute. Add half & half and chicken stock. Bring to a simmer and cook until sauce reduces and thickens, about 3-4 minutes. Add in shredded cheese and stir until cheese is incorporated. Season sauce if necessary.
Add drained pasta and spinach-chicken mixture to pan. Stir to combine.
