Please  submit your code here so the community can help you.
You can do it by inheriting _prepare_invoice as below:

Since you can create multiple invoices from one sale order you need to check if your field in invoice already has values to  not  move  them  each  time  you  create  invoice. 

def _prepare_invoice(self):
    self.ensure_one()
    res = return super([Your_Class_Name], self)._prepare_invoice()
    # Loop in your One2many field in sale order
    one2many_vals =[]
    for l in self.order_id.[Your_One2many]:
        one2many_vals.append(
        (0,0,{'One2many_column1_in_invoice_One2Many':l.[One2many_column1_in_sale_One2Many],
              'One2many_column2_in_invoice_One2Many':l.[One2many_column2_in_sale_One2Many],
              'One2many_column3_in_invoice_One2Many':l.[One2many_column3_in_sale_One2Many]
        }))
    res['One2many_field_name_in_invoice'] = one2many_vals
    return res