Substitute a can of fire-roasted tomatoes for 1 can of the diced tomatoes.
Do not be tempted to add the tomatoes first or to stir the ingredients. Tomatoes can scorch on the bottom of the cooker if added first.
In step 4, instead of using an immersion blender, you can transfer the soup, in batches, to a countertop blender. Be very careful when transferring soup, as it is very hot. Do not fill your blender more than halfway, to prevent hot soup from spewing out the top. After puréeing, return soup to the cooker.