Add the onions to the dutch oven and cook until softened and translucent. Then, add the garlic, tomato paste, oregano, cinnamon, and 1/4 tsp salt, and cook, stirring, for 2-3 minutes or until fragrant. Lastly, add the chipotle chilies, tomatoes, brown sugar, and bay leaf and bring to a simmer. Add the chicken breasts back into the pot and cover with the tomato mixture.