Ingredients

• 3/4 cup brown lentils, rinsed, strained and picked through
• 1 3/4 cups plus 1 tablespoon low-sodium vegetable broth or water
• 2 teaspoons extra-virgin olive oil
• 1 large red onion, half finely chopped and half thinly sliced
• Juice of 1/2 lemon
• Kosher salt
• 8 ounces fresh baby spinach
• 2 large cloves garlic, minced
• Freshly ground black pepper
• 1/2 teaspoon ground cumin
• 1 cup whole-wheat breadcrumbs
• 1/2 cup walnuts, toasted and finely chopped
• Cooking spray
• 6 whole-grain vegan hamburger buns
• Baby arugula, basil, roasted red bell peppers and spicy mustard, for serving, optional

Instructions

1. Bring the lentils and 1 3/4 cup of the broth to a boil in a medium saucepan over high heat. Reduce heat to medium-low, partially cover and simmer until the lentils are fully softened and the liquid is absorbed, about 30 minutes. Transfer to a medium bowl with the remaining 1 tablespoon broth and mash well with a potato masher. Set aside.
2. Heat the oil in a large nonstick skillet over medium heat. Add the chopped onion, lemon juice and 1/4 teaspoon salt and cook, stirring, until softened, about 6 minutes. Add the spinach, garlic, 1 1/2 teaspoons black pepper and cumin and stir until the spinach is wilted, about 3 minutes.
3. Add the spinach mixture, breadcrumbs, walnuts and 3/4 teaspoon salt to the lentils and mix thoroughly. Cover and refrigerate for at least 1 hour or overnight.
4. Preheat the grill to medium-high. Form the mixture into six 4-inch patties and spray with cooking spray on each side. Grill until nice grill marks form, about 3 minutes per side. Place the patties in the buns with the sliced onion and other toppings, as desired, and serve.