Apparently, when asked this question, Wolfram Alpha returns the rather surprising result of 1700 degrees Fahrenheit. Thanks to Shannon over at BBG for pointing this out.
And for what its worth, this whole Wolfram Alpha thing really isn’t all that impressive. Sure, it displays information in a more coherent way, but in terms of actually finding out information, I think there are better sources out there.
Maybe this one will change your mind: http://www97.wolframalpha.com/input/?i=2+slices+of+cheddar+cheese+and+1+tomato+and+30g+cucumber+and+a+leaf+of+lettuce+and+2+slices+of+white+bread