The BEST tuna salad

• 0.5 red onion, thinly sliced
• 0.25 cup red wine vinegar
• 2 tbsp extra virgin olive oil
• 1.5 tbsp balsamic glaze
• 120 g rocket
• 0.25 cup kalamata olives, pitted and roughly chopped
• 0.5 avocado, thinly sliced
• 280 g tin tuna chunks (in oil)
• 200 g tin chickpeas, drained
• 100 g cherry tomatoes, chopped
• 50 g Danish feta, crumbled