Bright and crisp, the acid in this dish is a great compliement to rich, fatty dishes.
Quarter the cabbage, discarding the hard core. Slice thinly and sprinkle with salt in a colander resting in a bowl. Set aside for 20 minutes.
Slice the onion thinly. Place in a bowl, cup or jar with the lemon juice. Set aside.
Mix the cabbage, parsley and onion (but not the lemon juice yet). Mix the vinegar, olive oil, and a pinch of salt. Dress the salad. Taste, and mix in lemon juice and salt slowly to taste. Think of the meal. If it's light, add less acid. If it will be heavy with starches and fats, add more acid to balance.