You can create from Automated actions .. settings>technical>actions while on developer mode. If you don't view this menu, you would have to install from Apps 'Automated Action Rules' module.

Create new:

Model - Lead/Opportunity
Trigger - On Update
Trigger Fields - Last Stage Update (crm.lead)
Domain - Is Won '=' Won

Action to do - Create Next Activity
You can then select the activity to be created and whom to be assigned and Due Date