Heat olive oil in a large cast iron skillet over medium-high heat until it shimmers. Cook for 1 minute before adding diced chicken breast to ensure proper browning and quick searing.
Sear the chicken for 4-5 minutes until golden on the outside, stirring occasionally. The chicken doesn't need to be fully cooked yet since this fall dinner will simmer together.
Add diced onion and minced garlic to the skillet, stirring for 2 minutes until fragrant. These aromatics build the flavor foundation for your cozy pumpkin base.
Pour in pumpkin puree, chicken broth, and heavy cream, whisking to combine smoothly. Add sage, thyme, nutmeg, salt, and pepper—this is where your cozy fall pumpkin skillet dinner transforms into pure comfort.
Reduce heat to medium and simmer for 12-15 minutes until the chicken cooks through completely. The sauce should bubble gently around the edges while the flavors meld together beautifully.
Stir in spinach and butter, cooking for 2-3 minutes until the greens wilt into the sauce. Top with parmesan cheese and serve immediately while everything steams.