Finely dice the onion, fry in oil and add the chanterelles, fry for about 10 minutes on a not too high heat.
Clean the lettuce and divide it on 4 plates. Drizzle a little with vinegar and oil (or, even better, spray with an atomizer). Pluck the parsley leaves from the bunch (put some leaves back for garnish) and roughly chop.
Season the fried mushrooms in the pan with salt, pepper, vinegar and mustard. Fold in the parsley and arrange the mushrooms on the salad. Garnish with a few parsley leaves.