Heat oil in a pan over medium heat. Add onion and cook for 2-3 minutes, stirring, until softened. Add garlic and ginger, and cook for a further minute. Stir in spices, then cook for 30 seconds until fragrant.
Add lentils, stock, tomatoes and 1 1/2 cups (375ml) water extra. Bring to a simmer, then reduce heat to low and cook for 1-1 1/2 hours, stirring occasionally, until the lentils are tender and dahl is thick and rich.
Stir through baby spinach.
Sprinkle with coriander (optional).
Notes
Serve with cooked rice and a dollop of mango chutney. Yum!