Looks like NuMex Big Jim

Mark

I agree with habajolokia It is likely pretty mild in heat (less than hot banana even). It may not be what you expected but they are very good peppers.
Bruce

Yep. Anaheim. Great looking pepper btw. Ought to make roasting and peeling a cinch.

Kevin

It's not easy to maintain seed purity when producing seed for commercial markets. Occasionally bees will pollinate your flowers with something that crosses with your target crop.

It may not be a particular variety, just a new cross or an odd bit of seed that got mixed in, no way to tell. If you like it, try to find more of them in your crop and save some seed from peppers you leave on the plants to ripen. It might breed true or it might not. Peppers are a highly variable plant genetically.