Start by rinsing lentils under cold water, then cook in boiling water for about 20-25 minutes until tender. Drain and let cool.

Heat a dry skillet over medium heat and toast chopped walnuts for about 5-7 minutes until fragrant and lightly browned. Let cool.

In a mixing bowl, combine cooled lentils, toasted walnuts, breadcrumbs, and spices. Add the egg or flax egg if using. Gently fold together.

With damp hands, scoop out portions and form patties about 3-4 inches in diameter. Adjust moisture as needed.

Preheat a non-stick skillet over medium heat, drizzle with olive oil, and cook the patties for 4-5 minutes on each side until golden brown.

Transfer cooked patties to a paper towel-lined plate, then serve on toasted buns with desired toppings.