Boil the pasta in salted water until al dente. Reserve 1/4 cup of the pasta water, then drain and set aside.
In a large skillet, heat olive oil over medium heat. Add minced garlic and stir it around until it smells amazing—about 30 seconds.
Toss in the shredded chicken and chopped spinach. Stir until the spinach wilts and the chicken is heated through.
Lower the heat and mix in the sour cream, cream cheese, mayo, onion powder, salt, and pepper. Stir until smooth and creamy.
Add the parmesan and half the mozzarella. Keep stirring until everything melts together into a glorious, cheesy mess.
Stir in the cooked pasta. If it looks a little thick, splash in that reserved pasta water to loosen things up.
Top with the remaining mozzarella. You can let it melt on the stovetop or pop it under the broiler for 2–3 minutes until golden and bubbly.
Spoon into bowls and watch it disappear faster than you can say 'what’s for dinner?'.