Combine first 8 ingredients. Add mayonnaise and mix well. Cover and refrigerate. Just before serving, mix breadcrumbs into salmon. Form into 4 patties. Melt butter in heavy skillet. Add salmon patties. Cook until golden and firm, about 3 minutes each side. Serve on toasted bread with Tarragon Mayonnaise, if desired. For Tarragon Mayonnaise, combine 1 cup mayonnaise, 1 Tbls lemon juice, 1 Tbls fresh chopped tarragon and 2 tsp Dijon mustard. Mix well.