Preheat large stainless steel pot or dutch oven on medium heat and swirl oil to coat. Add onion and garlic; cook for 3-4 minutes, stirring occasionally. Add red pepper flakes and bay leaf; cook for 30 seconds, stirring once.
Add tomato paste and mix well to combine. Add tomatoes, tomato sauce and stock; stir. Bring to a boil, cover and cook on medium for 20 minutes.
Add salmon and potatoes (optional but makes a more filling soup), cover and cook on low for 20 minutes. Add salt, pepper, lime juice and 3/4 of cilantro. Let stand for 5 minutes. Adjust any spices to taste if you wish. Serve hot garnished with fresh cilantro and extra lime.