Heat the oil in a non-stick frying pan. Toast the bread and sunflower seeds for approx. 3 mins. until golden brown, stirring occasionally, set aside.
Heat the oil in the same pan. Briefly brown the lettuce on both sides, season with salt.
Whisk the mustard with all the other ingredients up to and including the buttermilk, season.
Mix the cucumber and herbs, plate up along with the lettuce and cheese. Scatter the reserved croutons on top, drizzle with the dressing.