Spicy Red Lentil and Chickpea Stew

adapted slightly from http://www.kalynskitchen.com/2009/10/recipe-for-spicy-red-lentil-and.html

1 large onion, finely chopped (I think I used slightly less with no problem)
1 T canola oil
1 T finely grated fresh ginger
1 T finely minced garlic
1 tsp. ground turmeric
3/4 cup celery, finely diced (I used half of this because I didn't have enough around)
1 tsp. Garam Masala
1 1/2 tsp. ground cardamom
1/4 tsp. ground cayenne pepper
1 tsp. ground cumin
6 cups chicken, beef, or vegetable stock (I used 6 c water + bulk vegetarian bouillon powder)
1 1/2 cups red lentils
~2 cups cooked chickpeas or 1 can, rinsed
1 can (14.5 oz.) diced tomatoes, undrained

Heat oil in a heavy, big pot with a tight-fitting lid. Add onions, ginger, garlic, and turmeric and gently saute, stirring often, for about 7 minutes, or until onions are quite soft but not browned. Add diced celery, garam masala, ground cardamom, cayenne pepper, and ground cumin and saute 3-4 minutes more, until celery barely starts to soften.

Add the stock, red lentils, canned tomatoes, and chickpeas and bring mixture to a gentle boil. When it starts to bubble, reduce heat to the barest simmer and cover pan with lid. Let mixture simmer, stirring a few times, until lentils are dissolved enough that mixture has thickened into a chunky stew (about an hour.)