Offer offer offer.
My DS went through this with corn dogs when he was 2.5-3ish. That's ALL the kid wanted! I would give him as many appropriate choices as I could, both food wise and in daily life. For example, I'd tell him "you can have cereal or eggs with ketchup for breakfast". His response would be "I want a corndog instead." I'd tell him "Mmmm..A corn dog sounds really good. Let's have that for lunch and you can have eggs or cereal now." Usually it would work. If he wouldn't tell me which he wanted, or if he didn't waver from his corndog stance, I'd tell him "Well I'll tell you what, I'll choose for you. How about eggs...I think I'll have some too. For lunch we'll have corndogs". Then I would totally involve him in the cooking of the eggs...counting, cracking, sprinkling cheese. That worked like a charm!
Then I'd hold true and have corn dogs for lunch...Served with a side of veggies and dip or mandarin oranges or anything else I could come up with to add some nutrition. I'm happy to announce I haven't had to buy corndogs in 6 or 7 months...He's quite sick of them now! Relax. It's a small stage and it will pass. As my old, wise, wonderful Family Dr. said to me when I was in this boat..."It's your job to offer him healthy food, but it's his job to eat it!"
Good luck to you!
Rigama