Ask a Southern Californian where to get the best pastrami, and chances are likely they'll say "The Hat".
The Hat is a small chain of restaurants in SoCal that got started in 1951. I'm told their Alhambra location was the first, and I think their Lake Forest location is the newest.
Yesterday, I went to their Pasadena location.
One thing the The Hat is known for is large portions. Order a pastrami sandwich, or a pastrami burger, or get the chili fries, and more than likely you won't have room for much more.
If you order a side of fries, they take a brown bag about the size of a lunch bag, and fill it up. After eating your sandwich, you'll maybe only have room for a three of four pieces of french fries. The same is true when you order onion rings.
If you get about four of you going to The Hat, then only order ONE side of fries, and split it. That's what we did yesterday, and we still could not finish off the fries.
Visit The Hat online, and try their Pastrami Burger: