Heat the olive oil in a large pot over medium heat. Add the lamb cubes and cook until browned on all sides.
Add the onion, garlic, and ginger to the pot. Stir and cook until the onion softens.
Stir in the cumin, coriander, turmeric, and garam masala. Cook for one minute until the spices smell fragrant.
Add the rinsed lentils, diced tomatoes, and broth. Bring the mixture to a boil.
Reduce the heat to low, cover the pot, and simmer for 45 minutes. Stir now and then until the lamb and lentils are tender.
Add the spinach and stir until it wilts. Season with salt and black pepper to taste.