Rinse lentils under cold water. In a medium saucepan, combine lentils and water/broth. Bring to a boil, then reduce heat and simmer for 20-25 minutes until tender but not mushy. Drain well and set aside.

Heat olive oil in a skillet over medium heat. Add chopped onion and cook for 5 minutes until softened. Add minced garlic and cook for 1 more minute. Add spinach and cook until wilted. Remove from heat.

In a large bowl, combine the cooked lentils, spinach mixture, breadcrumbs, egg, cumin, smoked paprika, salt, and pepper. Mash with a fork or potato masher until about half the lentils are broken down. Do not overmix.

Divide the mixture into 6 equal portions and shape into patties about 1-inch thick. For best results, chill the patties in the refrigerator for at least 30 minutes to help them firm up.

To pan-fry, heat a little oil in a large skillet over medium-high heat. Cook patties for 4-5 minutes per side until golden brown. To bake, place on a parchment-lined baking sheet and bake at 375°F (190°C) for 20-25 minutes, flipping halfway through.