Place the eggs in a pan of cold water, bring to the boil then reduce the heat and simmer for 8 minutes until hard-boiled. Run under cold water to cool, then shell and cut in halve.
Meanwhile, cook the beans in a pan of boiling water for 4-5 minutes, until tender. Drain well and set aside.
Place the lettuce leaves ina large salad bowl, add the green beans, tuna and red onion. Drizzle with the dressing, then gently toss together to combine.
Top with the hard-boiled eggs and croutons and serve.