Create a Data Cloud Streaming Ingestion API Payload in Apex

String streamingIngestionPayload = JSON.serializePretty(new Map<String,List<Map<String,Object>>>{
    'data' => new List<Map<String,Object>>{
        new Map<String,Object>{
            'Id'      => 'id',
            'Number'  => 1234,
            'Boolean' => true,
            'Object'  => JSON.serialize([SELECT Id,Name FROM User WHERE Id = :UserInfo.getUserId()])
        }
    }
});

System.debug(streamingIngestionPayload);