The story goes, it was invented in Iowa at the "Happy Joe"'s chain. Now, I love Iowa, but they are not known for their pizza OR tacos.
However, this they got right. It is on almost all pizza menus around here, in Minnesota.
LOVE it.
Most bases are either salsa/taco sauce/refrieds with sauce mixed in. Then meat, cheese. Baked. After out of the oven, it is topped with the chopped lettuce, onion, tomato, black olive and crushed taco chips. Add some more taco sauce.
It is SOOOO delicious.