In a 10-inch to 12-inch saute pan, heat oil slowly over medium heat. Add onion and cook slowly until soft but not brown (about 10 minutes). Add livers, capers, anchovy fillets and red pepper and cook until lightly browned (about 10 minutes). Add wine and cook until only 3 to 4 tablespoons of liquid remain.
Pour liver mix into food processor and blend intermittently, leaving lumpy -- not smooth -- like a puree. Season with salt and pepper and remove to a small mixing bowl.
Peel cucumber and remove seeds. Slice into 1/8-inch half moons and dress with oil, vinegar, sugar and season with salt and pepper.
Grill or toast bread on both sides and spread 1 tablespoon duck liver mixture over each one. Divide among 4 plates. Place 2 tablespoons of cucumber mixture on each plate and serve immediately.