In a large pot, turn heat to medium.
Add cumin seeds until they "pop"/roast - usually 1 minute.
Add olive oil, celery, carrot, and onion.
Cook for 10 minutes, stirring occasionally.
Add garlic (and fresh ginger if not using powdered).
After 1 minute, add salt and pepper to taste.
Add broth, diced tomatoes, washed and drained lentils, bay leaf, and all remaining spices.
Cover for 15 minutes and simmer.
Reduce heat to low and simmer covered, another 15 minutes. Check in 10 minutes to see if lentils are soft.
Add spinach and vinegar.
Serve warm, when spinach is wilted.