In a large mixing bowl, combine cooked lentils, chopped spinach, breadcrumbs, optional Parmesan cheese, finely chopped onion, minced garlic, ground cumin, smoked paprika, and salt and black pepper to taste. Stir thoroughly.

Crack one large egg into the mixture, or use a flaxseed or chia egg for a vegan option. Mix until fully combined.

Divide the mixture into four equal portions. Shape each portion into a compact patty that is about 1 inch thick.

In a non-stick skillet, heat olive oil over medium heat. Place the patties in the skillet, leaving space between them.

Cook the burgers for 4-5 minutes on one side until golden-brown. Flip and cook the other side for an additional 4-5 minutes.

Remove cooked patties and serve on toasted buns with your choice of toppings.