Pat the cooked lentils dry with a clean towel. You want them as dry as possible to avoid mushy patties.
Heat 1 tablespoon olive oil in a skillet over medium. Add onion and a pinch of salt. Cook 4–5 minutes until softened.
Add garlic and cook 30 seconds. Stir in spinach and cook until wilted (2–3 minutes). Remove from heat and let cool slightly.
In a large bowl, mash the lentils with a fork or potato masher until about half are broken down. Leave some whole for texture.
Add the sautéed spinach mixture, oats, breadcrumbs, egg (or flax egg), soy sauce, tomato paste, smoked paprika, cumin, chili powder, salt, and pepper.
Stir until the mixture holds together. If it feels wet, add 1–2 tablespoons more breadcrumbs. If it feels dry, add 1 teaspoon olive oil or a splash of water.
Divide into 6 patties for burgers or 8 for sliders. Press firmly to compact.
Place on a parchment-lined plate and chill 15–20 minutes. This step helps the patties firm up and brown better.
Heat 1–2 tablespoons olive oil in a nonstick or cast-iron skillet over medium heat.
Sear patties 4–5 minutes per side until deeply golden and crisp at the edges. Don’t crowd the pan.
Transfer to a rack or paper towel. Taste one and adjust seasoning next batch if needed.
Toast buns. Add avocado or mayo, the patty, tomato, onion, pickles, and greens. Serve with baked fries or a simple salad.
