Transfer the lentil falafel mixture to the bowl of a food processor. To the lentil mixture, add the onion, egg, panko breadcrumbs through salt and pepper.
Shape the mixture into four 4- to 4½-inch patties, each about ½ inch thick. Heat a large frying pan or skillet over medium heat. Lightly coat the skillet with olive oil spray and add two of the falafel lentil veggie burgers.
To a small bowl, add the feta cheese, then use a fork to crumble it. Stir in the yogurt and mint, and add a touch of lemon juice if desired.