Preheat oven to 425°.
Cook beef and onion in a large nonstick skillet over medium-high heat until beef is browned, stirring to crumble. Drain well, and return beef mixture to pan. Stir in tomatoes and seasoning; cook over medium-high heat 1 minute or until thoroughly heated; set aside.
Unroll pizza crust dough. Press into bottom and halfway up sides of a 13 x 9-inch baking dish coated with cooking spray. Spoon beef mixture over pizza crust dough.
Bake at 425° for 12 minutes. Top with cheese, and bake 5 minutes or until cheese melts and edges of crust are browned. Let stand 5 minutes before slicing. Serve warm. Top with salsa and sour cream, if desired.