Heat the olive oil in a large skillet over medium-high heat. Add the Italian sausage and cook, breaking it up with a spoon, until browned and cooked through, about 5-7 minutes. Use a slotted spoon to transfer the cooked sausage to a plate, leaving the rendered fat in the skillet.

Reduce the heat to medium. Add the chopped yellow onion to the skillet and cook until softened, about 3-4 minutes. Add the minced garlic and cook for another minute until fragrant.

Pour in the chicken broth to deglaze the pan, scraping up any browned bits from the bottom. Stir in the heavy cream, chopped sun-dried tomatoes, Italian seasoning, and red pepper flakes. Bring the sauce to a gentle simmer.

Stir in the grated Parmesan cheese until it's melted and the sauce has slightly thickened. Season with salt and pepper to taste.

Add the uncooked gnocchi directly into the simmering sauce. Stir to coat, then cover the skillet and cook for 3-5 minutes, or until the gnocchi are tender and have plumped up (check package directions for specific timing).

Uncover the skillet and add the fresh spinach in large handfuls, stirring until it wilts into the sauce, about 1-2 minutes.

Return the cooked sausage to the skillet. Stir everything together until well combined and heated through.

Serve immediately, garnished with extra grated Parmesan cheese and a crack of black pepper if desired.