If the breasts are whole, split them. Cut each chicken breast half crosswise into 1/2-inch strips. In a large bowl, combine buttermilk, 1 T of the lemon juice, Worcestershire, soy sauce, paprika, pepper, and garlic. Add chicken strips and toss to coat. Cover and marinate at room temperater for 1 hour, or refrigerate overnight.
Preheat oven to 350F. Drain chicken well. In a large shallow bowl, toss bread crumbs with sesame seeds to mix. Roll chicken in crumbs to coat. Arrange in a single layer on a greased baking sheet. Drizzle melted butter over chicken fingers. Bake for 35 minutes.
Meanwhile, in a nonalluminum saucepan, combine plum preserves, mustard, horseradish, and remaining 1 T lemon juice. Melt over low heat, stirring, until smooth.
Serve chicken fingers hot or warm, with plum sauce for dipping, on the side.