Prepare the Vegetables:Remove the outer leaves from the cabbage and shred finely. Dice the cucumber, grate the carrots, and chop the red onion.
Flake the Tuna:Drain the tuna well and flake it with a fork into small pieces.
Combine Ingredients:In a large bowl, mix shredded cabbage, cucumber, carrots, onion, and tuna. Add cherry tomatoes or bell peppers if using.
Make the Dressing:In a small bowl, whisk together olive oil, apple cider vinegar, Dijon mustard, salt, and pepper.For a creamy dressing, whisk mayonnaise (or Greek yogurt), mustard, lemon juice, and garlic powder.
Toss and Serve:Pour your preferred dressing over the salad and toss gently until everything is evenly coated. Sprinkle herbs and seeds or nuts on top if desired.
Optional Chill:Let the salad sit for 10–15 minutes to meld flavors. Serve chilled or at room temperature.