We don't all have the skills of a Julia Child but almost anyone can put on a cooking class, even if complicated French cuisine isn't your speciality.
If you have access to a kitchen through your organization or can rent out a space that has one, you can put on a cooking class fundraiser in a number of different ways.
For example, you might want to cover the basics of cooking from the beginning, focus on a specific type of ethnic food, or look at putting together a holiday meal. Your class can cover one type of food (vegetable dishes or party appetizers perhaps) or a certain method of cooking (such as baking).
You'll have to limit the number of participants based on the size of your kitchen and each student pays a small fee to get involved. You might consider charging a lower fee for people who just want to observe (taking notes and picking up recipes). After the class you can all join together to share the fruits of your labors.
This is an idea that you can return to time and time again in the future by varying the topics and methods of cooking — use your imagination.