HEAT olive oil in large, heavy-duty saucepan. Add sliced cucumbers; cook, over low heat, stirring occasionally, for 3 to 4 minutes. Add leek, dill and bay leaf. Cook, stirring occasionally, for 20 minutes or until cucumbers are tender.
STIR in flour until absorbed. Add water, bouillon and pepper; simmer gently, stirring occasionally, for 30 minutes. Remove from heat. Stir in evaporated milk. Let stand for 30 minutes. Stir in lemon juice and remove bay leaf.
TRANSFER half of soup into blender container; cover. Hold down lid with folded towel. Blend until smooth. Pour into large bowl. Repeat with remaining soup. Cover; refrigerate for at least 1 hour. Stir in chopped cucumber. Season to taste with salt and pepper. Garnish with additional fresh dill, if desired.