Heat one tablespoon of olive oil in a skillet over medium heat. Add the chopped onion and cook until softened, about 4-5 minutes. Add the minced garlic and cook for another minute until fragrant. Remove from heat and let cool slightly.

Wilt the fresh spinach in a dry pan or in the microwave. Transfer the wilted spinach to a clean kitchen towel and squeeze firmly to remove all excess liquid. Roughly chop the spinach.

In a food processor, pulse the cooked lentils 4-5 times to break them down slightly, leaving texture. Transfer to a large mixing bowl. Add the cooled onion mixture, chopped spinach, egg, breadcrumbs, parsley, oregano, cumin, paprika, salt, and pepper. Mix with your hands until just combined.

Cover the bowl and chill the mixture in the refrigerator for at least 30 minutes. Once chilled, divide the mixture into six equal portions and form into thick patties.

Heat the remaining tablespoon of olive oil in a skillet over medium-high heat. Carefully place the patties in the hot skillet and sear for 4-6 minutes on the first side, until a deep golden-brown crust forms. Flip and cook for another 4-5 minutes on the second side until firm.

In a small bowl, combine the Greek yogurt, chopped dill, lemon juice, and minced garlic. Stir until smooth and season with a pinch of salt. Serve with the burgers.