While not necessarily a burger recipe there is a recipe that I am currently using in my restaurant with red lentils. If you boil some red lentils but make sure they are just barely cooked.. there is a very small threshold here, too cooked and the recipe is screwed, not cooked enough and you are eating raw lentils. Anyhow, once you get the lentils cooked right you just blend some cashew nuts, garlic, ginger, red onion, coriander and mint then add that blended mix to the red lentils with some salt. Not an exact recipe I know but you would want about 1/5th the amount of blended cashews for your amount of red lentils then the other ingredients are just for flavouring.
Best of luck!