This is not possible in ONE step without customization.

(for information about the customization, skip to PART B of this answer)

PART A:

A LOT in Odoo requires a Product, and the import does not currently support creating LOT records AND linking them to the correct product AND setting the quantity for the product ALL at once.

You need to import your LOT for PRODUCT records first, then import your INVENTORY ADJUSTMENT LINES.

You CAN use the same file though**, you just import it TWICE. The first time to create the LOT records, the second time to create the INVENTORY ADJUSTMENT LINE records.

** Your file should not refer to the same LOT twice.  If you have the same lot in two different locations, you should generate a second file of UNIQUE lot numbers to use during the import to create LOTS.  In your example (or if there is just a single location in the warehouse) then you can use the same file.

To master importing data into Odoo, you first create a single record and export it – this way Odoo will generate the “template” file for you.

Note: Advanced options are available during imports if you are in Developer Mode, so be sure to activate it before starting.

1. Create a new Inventory Adjustment:

2. Click START INVENTORY and click CREATE to enter the first line:

Note: you will be creating the LOT A at this time.  During the import however, you can elect to have LOTS created at the same time as the Inventory Lines.

3. Click SAVE then select the line and from the ACTION menu, choose EXPORT:

Be sure to select the option to create an import-compatible export, and click EXPORT:

You will get an XLS or CSV file like this:

4. Add the additional lines to that same file and save it.   Don’t worry about the ID field in the first column (You can actually DELETE this field) as you need this only if you plan to UPDATE information during your import, not create it. 

Note: for more information on how the ID field impacts data imports, see https://www.odoo.com/documentation/user/13.0/general/base_import/import_faq.html

6. Since the first line of your file matches the adjustment line you already created, you now want to DELETE it from Odoo so not to duplicate it when you import it:

7. Click IMPORT and LOAD FILE to use your file:

8. Verify your adjustment, then click VALIDATE INVENTORY to bring the numbers in:

When you run your Inventory Report, you will see your updated quantities by LOT:

PART B:

To customize Odoo to support the creation of LOTS that do not exist DURING the import, create a new field Outside Lot like this:

Then create an Automated Action something like this:

for record in records:
  lot = env['stock.production.lot'].search([('name','=',record.x_prod_lot_new),('product_id','=',record.product_id.id)])
  if lot:
    record['prod_lot_id'] = lot.id
  else:
    new_lot = env['stock.production.lot'].create({'name': record.x_prod_lot_new, 'product_id': record.product_id.id})
    record['prod_lot_id'] = new_lot.id

This directs Odoo to use the information from the Outside Lot field (which you will map to INSTEAD of the Lot ID field during your import) to check if you have an existing LOT record with that name / product combination and if you don't, create it at the time of the import of the adjustment line.

Note: This customization will work with LOTS that already exist inOdoo as well as those that don't and will not interfere with Inventory Adjustments that are created via the UI (not via import).  

When you do this process via the UI, the LOT can be created during the Adjustment.