Preheat oven according to pizza shell package directions. For mushroom sauce, in a medium saucepan heat the 2 teaspoons light butter with oil over medium heat. Add mushrooms, onion, and garlic; cook about 5 minutes or until tender, stirring occasionally. Add the 2 tablespoons light butter with oil to mushroom mixture. Stir in flour; cook for 1 minute. Gradually stir in milk. Cook and stir until thickened and bubbly. Stir in 1/2 cup of the cheese.
Spread mushroom sauce over pizza shell. Top with chicken, tomato, spinach, and the remaining 1/4 cup cheese. Bake according to pizza shell package directions (about 10 minutes). Sprinkle with basil. Cut pizza into wedges.