Here is a rough draft that you can suitably amend to meet your specific requirements.
Invitation to Diwali Lunch
Dear Friends,
Sub: Invitation to Diwali lunch on _____date at ______venue at ______time.
To celebrate and revel in the fun of Diwali, we have organized a lunch for all employees on _____date. Each one of you is invited to join in the celebrations and lunch to be held at _____venue from ___time.
To enhance the festivities, we encourage you to be dressed in your traditional best and also come prepared to display your talents and skills. You will be pleased to note that we have also arranged for ________ (if you have additional plans).
We look forward to commencing the Diwali season celebrations with joy, fun, laughter, great bonding, and camaraderie, and this is only possible with your presence and active participation. We eagerly anticipate your joining us and together having a wonderful Diwali celebration.
With warm Diwali Greetings,
XYZ
P.S. In case anyone is unable to join for any reason, please communicate your regrets to the nominated person/coordinator of the Diwali party.
Hope you all have a great response and a wonderful Diwali party.
Happy Diwali to each one of you.
Warm regards