Coat a 15 x 10-inch jelly-roll pan with cooking spray, and sprinkle with cornmeal. Unroll pizza dough, and press dough into pan. Bake at 425° for 6 minutes or just until crust begins to brown.
Combine spinach, mozzarella cheese, garlic, Italian seasoning, and pepper in a bowl; stir well. Spread spinach mixture over crust, leaving a 1/2-inch border. Top with mushrooms and tomatoes; sprinkle with feta cheese. Bake at 425° for 9 minutes or until crust is lightly browned (feta cheese will not melt). Cut into 6 equal pieces.