Heat butter in a large skillet, over medium heat. Sauté onion and apple until soft, about 5 minutes.
Stir in garlic, curry powder, and thyme, cook 2 minutes longer. Remove from heat.
Add ground chicken, lentils, panko, mustard, egg, salt, and pepper in a large bowl. Stir just to combine. Cover and refrigerate 1 hour.
Shape burgers into 6 patties.
Preheat and brush grill with canola oil. Cook burgers 6-7 minutes per side over medium high heat. Flip once. Cook until no longer pink in middle.
Serve on hamburger bun, and top with condiments as desired.