Thaw salmon, if frozen. Rinse; pat dry with paper towels. Sprinkle with the 1 to 2 teaspoons chili powder and the 1/2 teaspoon salt. Cover and refrigerate while roasting vegetables.
Preheat oven to 425 degrees F. Place sweet peppers, onion, and jalapeno pepper, cut sides down, on foil-lined baking sheet. Roast for 15 to 20 minutes. Loosely wrap vegetables in foil; let stand for 15 minutes.
Meanwhile, place salmon in a shallow greased baking pan; fold under thin edges. Bake for 4 to 6 minutes per 1/2-inch thickness or until salmon flakes easily when tested with a fork; keep warm.
With a sharp knife loosen and peel off skins from peppers; discard skins. Coarsely chop peppers and onion; transfer to a large saucepan. Add broth and canned tomatoes. Bring to boiling, stirring occasionally. Remove from heat. Season to taste with salt and black pepper. Fold in chopped tomato and parsley.
To serve, ladle chowder into shallow bowls. Break salmon into pieces and divide among bowls. Top with avocado slices and sprinkle with additional chili powder.