When I lived in Fairfield and Jessie would come to visit every few weeks, one of her favorite things to do in town was to go to Small Planet Cafe and have a cheddar walnut burger. We both agreed it was delicious and had a great texture. On our last visit to the restaurant I asked for the recipe, only to find that the burgers were a frozen product made in Minnesota! This appears to be it: http://www.walnutburger.com/ We were disappointed, not least because Small Planet claimed to be inspired by the famous cookbook, which rails against mass-produced foods.
Then we moved to Kansas, and the restaurant went out of business, and we got to missing the walnut burgers, and I searched for a recipe online. Here's the one I found: http://www.tasteofhome.com/recipes/Cheesy-Walnut-Burgers We've been very happy with this recipe, and it's one of our favorites (when we get around to using a recipe). The only disadvantage is that there are a lot of ingredients, so preparation takes about as long as cooking. You could probably get around that by using less fresh ingredients and mixing them in advance, so that only the egg and ketchup needed to be added, but I'm sure the burgers wouldn't taste as good if you did that.
One thing to watch out for: be sure to use soft bread crumbs, not cracker crumbs. If you only have cracker crumbs, add more egg -- not water -- to compensate, or the burgers won't stick together.
We usually use regular pepper and a dash of lemon juice in place of lemon pepper, since we don't keep lemon pepper on hand. I've been known to use wood sorrel in place of lemon juice. :-)