Combine salmon and next 3 ingredients in a stainless steel or glass bowl. Cover and refrigerate 2 hours. (Salmon will be opaque on the outside and translucent pink inside.) Drain all but 1/4 cup of juice.
Broil chiles on an aluminum foil-lined baking sheet 5 inches from heat (with electric oven door partially open) about 5 minutes on each side or until peppers look blistered. Let stand 10 minutes. Peel peppers; remove and discard seeds and stem. Cut into 1/4-inch pieces, and stir into salmon mixture.
Peel orange with a sharp knife to remove rind and white pith. Cut into segments, discarding any seeds. Halve segments; add to salmon mixture. Stir in capers, cilantro, and salt. Cover and refrigerate until ready to serve.
Divide the frisée among 8 martini glasses or serving bowls. Spoon seviche into center of frisée; garnish, if desired. Serve with crackers or crostini.