First chop up the sweet potatoes, red pepper, tomatoes and set aside so they don't hold you up.
Heat butter (optional, can skip butter) and olive oil in heavy, large sauce pan and cook onion, 2 or 3 scallions and shallots over low heat for 5 minutes.
Add the garlic and chopped red pepper and tomatoes and continue cooking stirring occasionally, for 5 minutes or until the tomatoes become pulpy.
Add the clam juice, add some extra water to cover if needed. Bring the liquids to a boil.
Add the sweet potatoes, thyme, chives (or more scallions). Add some salt and black pepper, about a tsp or so of each. Lower the heat and let the mixture simmer gently for about 15 minutes or until the sweet potatoes are just tender but not too soft.
Add the skinned salmon and let the mixture return to a boil but then lower heat. Spoon some of the chowder over the salmon or push below surface, then lower the heat and cover the pan and cook for 3 minutes. The salmon cooks fast and all the way through so don't let it go for too long. If you forgot to skin the salmon you can place on top of broth, skin side up, spoon broth over it, cover and then peel skin off when cooked to loosen.
Let the salmon cook over medium-low heat for 3 minutes. Taste for seasoning, add salt if necessary and ladle into bowls. Sprinkle chopped scallions on top.