Whisk the mustard, vinegar, 3 tbsp oil with 1 tbsp of water and a pinch of salt to make a dressing.
Heat the grill to high, scatter the bread on a baking tray and drizzle with the remaining oil. Put on the bottom of the grill and toast for 8-10 mins, tossing every couple of mins until well done.
While the croutons are toasting, boil the beans for 3-5 mins until cooked but slightly crunchy. Scoop them out using a slotted spoon and toss them in a bowl with a little dressing. Lower the heat under the water, add the haddock and gently poach for 5 mins. Lift the fish onto a plate, add a splash of vinegar to the water, break in the eggs and poach them for 3 mins. Lift them onto a piece of kitchen towel to drain.
Tip the leaves into a large bowl and flake over the haddock in large chunks. Add the croûtons and beans plus most of the dressing, then toss everything together. Pile onto 2 plates, top with the eggs, drizzle with the remaining dressing and eat while it’s still warm.