Mix all ingredients except the oil and fixings together in a medium bowl. Form into 4 patties. Chill at least 20 minutes and up to 1 day, covered.
Heat oil in a large nonstick frying pan over medium heat. Cook burgers, turning only once, until browned and hot inside, about 5 minutes total.
Serve each patty with fixings.
*Find cooked lentils in vacuum packs at Trader Joe's or other well-stocked grocery stores.