Begin by bringing a large pot of salted water to a rolling boil. Once boiling, add spaghetti and cook according to package instructions until al dente, about 8-10 minutes. Drain and set aside.

In a large skillet over medium heat, pour olive oil and let it heat. Season chicken with salt and pepper, then place in the skillet. Cook for 5-7 minutes on each side until golden brown and fully cooked through. Remove chicken, let rest, and slice.

Using the same skillet, add onions and garlic, cooking for 2-3 minutes until onions become translucent and fragrant.

Pour in chicken broth and bring to a gentle simmer, cooking for about 3 minutes. Then, reduce heat and add heavy cream and shredded Monterey Jack cheese, stirring until cheese melts.

Next, stir in cherry tomatoes and spinach. Cook for another 3-4 minutes, until spinach wilts and tomatoes soften.

Add sliced chicken and cooked spaghetti to the skillet. Gently toss everything together until pasta is well-coated with sauce.

Taste and adjust seasoning with salt and pepper. Plate the spaghetti, sprinkle with Parmesan cheese if desired, and garnish with parsley or cilantro.