In a large heavy duty dutch oven, heat olive oil over medium heat. Add onion and red bell pepper; saute the vegetables for 8 minutes or until soft and lightly browned, stirring occasionally.
Stir in garlic and chili powder; cook for 1 minute.
Add lentils, tomatoes, bay leaf and stock. Season with salt and ground black pepper, to taste. Bring to a boil, lower the heat to medium-low and simmer, partially covered for 30 minutes or until lentils are tender. Remove from the heat and discard the bay leaf.
Transfer 3 cups of cooked chili into a food processor and process until pureed; add the pureed chili back into the remaining chili and stir to combine. Taste for salt and pepper.