Put the Alfredo sauce in a pot over medium-low heat and let it come to a simmer. Add the spinach and stir until just wilted; turn off the heat.
On each toasted muffin half, spread 1/4 cup Alfredo sauce, a sprinkle of Italian seasoning, a portion of the chicken and some mozzarella. Bake on a baking sheet until the cheese is melted, about 5 minutes. Serve warm.