Blanch snow peas in lightly salted boiling water for 1 minute. Immerse in iced water; drain.
Tear lettuce into pieces. Distribute among serving bowls. Add snow peas; sprinkle with spring onions.
To make the vinaigrette, whisk oil, vinegar and a generous seasoning of salt and pepper. Drizzle over salad greens. Sprinkle with beansprouts.
To make the croutons: cut the bread into small cubes. Heat the butter in a nonstick frying pan over medium heat. Add the garlic, cut surfaces face down. Fry 30 seconds, remove from pan and discard. Place bread cubes in garlic butter and cook until golden brown on all sides, taking care so the butter does not burn. Serve the salad topped with hot croutons.