Cut the Lyoner first into thin slices and then into fine strips. Cut the Gouda into strips. Peel, quarter and thinly slice the onions. Quarter the cucumber lengthways and cut into 1/2 cm pieces without peeling. Drain the corn. Weigh the parsley finely. Dice the peppers. Mix all ingredients in a bowl.
For the dressing, mix the ketchup with the mustard, vinegar, stock and oil well. Season to taste with salt, pepper and cayenne pepper. Pour the dressing over the salad, mix gently and let it steep for at least 30 minutes.