Brush the bread slices with 1 tbsp. olive oil and grill until crispy. Peel and finely chop the garlic, then mix with the lemon juice, 3 tbsp. oil, vinegar and mustard to make a vinaigrette. Season with salt to taste. Halve the lettuce hearts and brush them with 1 tbsp. oil. Place them flat-side down on the grill and grill until grill marks appear. Cut the spring onions into fine rings and arrange them on plates with the lettuce hearts. Break the bread into croutons, add them to the plates and drizzle with the vinaigrette.