Dab the fillet dry. First cut into small cubes, then chop them crisscross. Peel onion and dice very finely. Mix fillet, onion, capers, sambal oelek, 4 tablespoons olive oil and mustard. Season well with salt and pepper.
Toast bread in a toaster. Brush with butter.
For the scrambled eggs, whisk eggs and milk. Season with salt and pepper. Heat 2 tablespoons of oil in a large frying pan. Add the egg milk and let it set, pushing it together from time to time. Spread the tartar and scrambled eggs on the slices of bread.
Garnish with salad and caper apples.