Tuna traybake recipe with herby salsa verde dressing

Name: Tuna traybake recipe with herby salsa verde dressing
Ingredients: 2 red onions, each cut into 8 wedges through the root; 350 g new potatoes, halved if large; 150 g green beans, stalked ends trimmed; 1 tbsp. olive oil; 1 tbsp. dried oregano; 1 each red and yellow pepper, deseeded and sliced; 100 g pitted black or green olives; 350 g cherry tomatoes; 4 g tuna steaks; 50 g rocket; 20 g pack parsley, leaves picked; 2 anchovy fillets in oil, drained; 1 garlic clove, crushed; 1 tbsp. extra virgin olive oil; 1 tbsp. capers, drained; 1 tbsp. Dijon mustard; 1 tbsp. red wine vinegar