help!!! going out to eat & I don't want to ruin my healthy eating!?

Ok so im vegetarian and im on a diet.and im going to dinner with freinds tonight. The place they chose is called fuddruckers and I looked at the menu online and they are famous for there build your own burger thingI guess there is a topping bar. They have veggie burgers but is it healthy for me to eat a white bun? I was going to get a veggie burger with mustard and load it with veggies . Is the bun ok though?
 
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