To be honest, strawberry may one of the less offending things that I've seen in a burger.
Went to a fancy burger place and one of the choices was a burger with tuna and anchovies. I almost threw up.
But a burger with side mushrooms, with chocolate covered peaches, with a fruit salad, and even weirder things have passed before my eyes to my great regret.
Compared to this an Hawaiian pizza is trivial. Once in Spain I was served a burger that wasn't only gigantic in width it was also covered in sauces that should never be near a burger. I ate it, but it was a torment and only after I removed the half a kilo of tomatoes and olives. It was a 2 hours affair. It took me a liter of beer to wash it all down. In a "American Style" burger joint I was served a "special" burger with the fries INSIDE it. Not that it wasn't tasty, but it made the whole affair unbalanced in taste.
A sliced strawberry on the side? Bah, you can chalk it down to plate decoration and you don't have to eat it. There are truly horrendous things out there...
Peace