The roasted garlic adds a richness to the smoky heat of the chipotle peppers in this hearty(and yummy!) soup. It improves as the flavors delvelop, so go ahead and make it a day or two ahead! Adapted from Fields of Greens cookbook.
To toast cumin (or coriander) seeds, place the whole seeds in a dry small skillet over low heat. Stir and shake until the seeds release their aroma and darken slightly, just a minute or two. Transfer to a bowl if you won't be grinding them right away, they will continue to cook if left in pan. Grind in a spice grinder or mortar and pestle.
Sort and rinse the lentils and put them in a soup pot with the water, bay leaf, sage, and oregano. Bring the water to a boil, reduce the heat, and cook, uncovered, at a gentle boil for 15-20 minutes, until the lentils are tender. Remove the herbs.
While the lentils are cooking, preheat the oven to 350*F. Rub the head of garlic with a little oil, place on a baking sheet, and roast for about 30 minutes, until soft. When the garlic has cooled, slice off the top of the head and squeeze the garlic out of its skin. Puree with the tomatoes in a blender or food processor and set aside.
Heat the remaining oil in a large saucepan. Add the onion, 1/2 teaspoons salt, cumin, and dried oregano; saute over medium heat until the onion is soft, about 7-8 minutes. Add the carrot and peppers and saute until tender, about 5 minutes. Add the ancho chili powder and the chipotle puree, the pureed tomatoes, and 1 teaspoons salt; simmer for 10 minutes.
Combine the lentils and their broth with the vegetables, cover and cook over low heat for 30 minutes. Add salt to taste. For more spice, add more ancho chili powder or chipotle puree to taste. Sprinkle in the fresh cilantro and oregano just before serving.