I love a classic diner burger with American cheese, pickles, mustard and ketchup. This is definitely not a classic but if you are going to change things up on the burger: pineapple and a sweet teriyaki sauce are amazing. I first had these burgers camping with some friends and ever since, they have been on the short list for my favorite burgers. Doing these on the pellet grill adds an extra shot of flavor to the pineapple.
I was recently watching an episode (SE03 EP10) of Man Vs. Food on Netflix. Adam, the shows host, was trying to eat a 5 pound smoked meat hoagie in Kansas City called the Destroyer. He ultimately failed the challenge and blamed it on the smoked hamburger patties. He said that the sandwich was great but the burger was just too dry. The moral of this story is, "Don't slow smoke your burgers!" Get your grill nice and hot so you can grill them up quick and juicy.