Clean, wash and cut the spring onions into rings. Mix lemon juice with sugar, salt and pepper, fold in oil. Wash and clean the tomatoes and cut off the lids. Remove the seeds. Cut avocados in half, remove seeds.
Remove the flesh from the skin and cut into small pieces. Mix avocado pieces, spring onions and vinaigrette. Fill tomatoes with avocado salad. Arrange on a plate, garnish with basil leaves and serve immediately