In a covered saucepan, cook potatoes in boiling salted water for 12 to 15 minutes or till just tender; drain well. Meanwhile, prepare the Walnut Vinaigrette.
Remove skin and bones from smoked salmon. Coarsely flake; set aside.
In a large mixing bowl combine drained potatoes and sweet pepper strips. Pour half of the Walnut Vinaigrette over the potato mixture. Toss lightly to coat.
To serve, arrange romaine on 4 dinner plates. Top with radicchio and potato mixture on top of the romaine. Sprinkle with walnuts. Arrange salmon on top. Drizzle with remaining Walnut Vinaigrette. Serve immediately. Makes 4 main-dish servings.
In a screw-top jar combine walnut oil, white wine vinegar, shallot, water, sugar, chives, brown mustard, sea salt, and hot pepper sauce. Cover and shake well. Serve immediately or cover and store in refrigerator up to 1 week. Shake just before serving. Makes about 1-1/4 cups.