Young Broadbean Salad with Tuna Fillets in Olive Oil

Name: Young Broadbean Salad with Tuna Fillets in Olive Oil (Salada de Favinhas Novas com Filetes de Atum em Azeite)
Yield: Serves four
Cuisine: Portuguese
Ingredients: 1 medium red onion; 2 tablespoons fresh coriander; salt and pepper; 16 cherry tomatoes, halved; olive oil; 4 cups young broadbeans, peeled (about 400 g); 1 tablespoon of fresh mint leaves; 2 handfuls mixed lettuce leaves; 3 cans tuna fillets; 1 lime, juice and zest; red wine vinegar; croutons to taste; sesame seeds, toasted