Start by cooking the fettuccine according to package instructions; drain and set aside.
While the pasta is cooking, season the chicken breasts with Cajun seasoning, salt, and pepper on both sides.
In a large skillet, heat the olive oil over medium heat. Add the seasoned chicken breasts and cook for about 6-7 minutes on each side, or until fully cooked and golden brown. Remove from the pan and let them rest before slicing.
In the same skillet, add the chopped onion and sauté for 2-3 minutes until translucent.
Add the minced garlic and cook for an additional minute, stirring until fragrant.
Pour in the chicken broth and stir to deglaze the pan, scraping any bits off the bottom. Allow it to simmer for about 2 minutes.
Lower the heat and mix in the heavy cream, stirring until fully combined.
Add the halved cherry tomatoes and spinach, cooking until the spinach is wilted and the tomatoes are slightly soft.
Toss in the cooked fettuccine and sliced chicken, mixing everything well to combine and heat through. Adjust seasoning with additional salt and pepper if necessary.
Serve warm, topped with grated Parmesan cheese and a sprinkle of chopped parsley for garnish.
Notes
Adjust seasoning to taste and serve immediately for best flavor.