"Cheese and Tomatoes" are a common source of humor that Walter refrences to express difference of others. The joke was first mentioned in 1970s Going Nowhere, No place, and No admission;
"He's going to Brazil, and he went to Rio de Janeiro last year. Them places are different"-Walter
"What difference does it make?"-Xenophanes
"It's as different as Cheese...and tomatas. Different as different can be.-Walter
-Walter and Xenophanes talking about The Spring Penguins trip to Brazil
As Walter pronnounces it, tamatas. However, he did express the food being similar in 1996 To live and die in Dixie;
The difference between Mexico and Russia are Cheese and Tomatoes.-Xenophanes
You can't say that. Their differences make pizza-Walter