How to specify nested blocks for StreamField default value?

I'm using Wagtail/CodeRedCMS to develop a site for a non-profit org. I have a custom EventPage class that inherits from CoderedEventPage. I would like to pre-populate new Event pages with a default set of nested blocks: Body->Responsive Grid Row->Column->Text. I have learned that this is possible by setting the default property on the StreamField object, and I have been able to use this successfully to pre-populate with a single child block. However, I can't figure out how to get it work for a nested structure.

I have gotten as far as the following within the EventPage class:

body = StreamField(
    LAYOUT_STREAMBLOCKS,
    null=True,
    blank=True,
    use_json_field=True,
    default=[
        ("row", {
            "content": [
                ("text", {"value":"foobar"})
            ]
        })
    ]
)

This doesn't throw an error like some of the other default values I tried, but it only half works.

What I expect/hope to see when adding a new Event page in the admin interface: new Event page with pre-populated body

What I see using the above code: new Event page with partially populated body

The Responsive Grid Row is pre-populated, which is partial success, but the column and text box are not. I understand that my default value is not quite right, but I can't seem to wrap my head around how to correctly specify it. Any help is appreciated.

You want to make the basic structure look something like this, but it seems this is a little problematic nevertheless.

body = StreamField(
        LAYOUT_STREAMBLOCKS,
        null=True,
        blank=True,
        use_json_field=True,
        default=[
            ("row", {
                "content": [
                    ("content", {"content": [("text", "Foobar")]})
                ]
            })
        ]
    )

In particular, you need to consider the GridBlock, ColumnBlock and each of the Streamblocks inside them.

Also, it seems that the stream blocks need the stream child defaults in the format {"type": "...", "value": "..."}

body = StreamField(
        LAYOUT_STREAMBLOCKS,
        null=True,
        blank=True,
        use_json_field=True,
        default=[
            {
                "type": "row",
                "value": {
                    "content": [
                        {
                            "type": "content",
                            "value": {
                                "column_size": "",
                                "content": [
                                    {
                                        "type": "text",
                                        "value": "Foobar"
                                    }
                                ],
                            }
                        }
                    ],
                }
            }
        ]
    )