public class ComplexObjectOverride : ILuceneMappingOverride<ComplexObject>
{
    public void Override(LuceneMapping<ComplexObject> mapping)
    {
        mapping.Map(x => x.Title).Store(Field.Store.YES);
        mapping.Map(x => x.ListOfItems).Format(x => FlattenList(x)).Store(Field.Store.YES).Index(Field.Index.ANALYZED);
    }
}

var index = new FluentIndexWriter<TestObject>(dir, analyzer, maxFieldLength);
    index.AddDocument(new TestObject() { ... });