Simple and nourishing, this is one of my go-to soups. Play around with different vegetables as you like (chard or kale for the spinach, etc.), and add more or less broth to your taste. Additional spices and flavors might include cumin, turmeric, or even a bit of coconut milk.
In a large soup pot over medium heat, warm the olive oil. Add the onion, carrots and celery, and cook until soft about 5-7 minutes. Add a splash or two of water if needed. Stir in the dried spices, cover the pot, reduce heat to simmer, and cook for another 5 minutes.
Add the split peas and the vegetable broth. Bring to a boil, then lower and simmer, half-covered, for 1 to 1 ½ hours. Add water as necessary if the split peas absorb too much broth, or you prefer a more brothy soup.
Test split peas; when fairly soft, stir in the spinach and cook until wilted. Season with salt and pepper.
Soup can be stored in a glass air-tight container in the fridge for 3 days.