Cook the pasta according to package instructions until al dente, then drain.
While the pasta cooks, heat the olive oil in a large skillet over medium-high heat.
Add the diced chicken thighs to the skillet, season with salt and pepper, and cook until browned.
Stir in the diced onion and cook until softened, followed by the minced garlic.
Pour in the heavy cream and bring to a simmer, stirring to combine.
Add the sun-dried tomatoes and cooked pasta to the skillet, tossing to combine.
Fold in the baby spinach and let it wilt, then adjust the seasoning if necessary.
If the sauce is too thick, add reserved pasta water a little at a time while stirring.
Serve hot, topped with grated Parmesan cheese.