Cook pasta according to package directions. Reserve ½ cup pasta water before draining.
While pasta cooks, heat olive oil in a large skillet over medium heat.
Add garlic and cook 30 seconds.
Add tomatoes and cook 3-5 minutes until softened.
Add the chicken and heat through.
Stir in spinach until wilted.
Add the cooked pasta and a splash of pasta water. Toss everything together.
Mix in Parmesan, black pepper, and red pepper flakes if desired.
Taste and add a little salt if needed.