01 - Combine lentils and water in a medium saucepan. Bring to a boil over high heat, then reduce heat to medium-low and simmer uncovered for 20-25 minutes until tender. Drain any excess water and set aside.
02 - While lentils are cooking, heat olive oil in a large skillet or pot over medium heat. Add cumin seeds and toast for 30 seconds until fragrant, watching carefully to prevent burning.
03 - Add chopped onion to the skillet and sauté for 4-5 minutes until soft and translucent. Stir in garlic and ginger, cooking for 1 minute until fragrant.
04 - Add diced tomato, turmeric, coriander, garam masala, chili powder, salt, and black pepper. Cook for 3-4 minutes, stirring frequently, until tomatoes break down and spices become aromatic.
05 - Add the cooked lentils to the skillet and stir well to incorporate. Cook for 5 minutes over medium heat, allowing flavors to meld. Add a splash of water if the mixture becomes too thick.
06 - Reduce heat to low. Gradually stir in Greek yogurt, adding it slowly and stirring constantly to create a smooth sauce. Heat gently for 2-3 minutes until warmed through, being careful not to boil which can cause curdling. Taste and adjust seasoning as needed.
07 - Stir in baby spinach if using and cook for 1-2 minutes until just wilted. Remove from heat immediately.
08 - Serve hot while fresh, garnished generously with chopped cilantro and accompanied by lemon wedges for squeezing over the top.