With a teacher experienced in identifying edible weeds, several activities are possible across the levels.
A good resource book like this one can be helpful. You could use it for your own information or adapt it for higher level learners.
You could
1. Talk about learners' own experiences foraging for and growing food. Do TPR to connect actions and vocabulary. See this link for some ideas for Phase I learners on using TPR and song for learning new vocabulary: https://www.youtube.com/watch?v=MJuOR9jTpV4
2. Talk about foraging in Canada - do people do it? Where? Why? What times of year?
3. Collect some edible leaves and flowers and have your students take photos of them, or trace / draw them.
4. Compare shapes, sizes and colours of leaves and flowers.
5. Take your class on a walk around the block to pick your own salad. Follow or make a map while you are at it!
6. Sample all the edibles and describe the taste, texture, and smell.
7. Have a local guest speaker come to class and talk about edible weeds.
8. Read a flyer (adapted as necessary) about a course on this topic: http://haltonenvironment.net/?tribe_events=eat-your-weedies-2
9. Find and follow some recipes using edible weeds. Write your own recipe.
10. Read and discuss issues around excessive foraging / harvesting (adapted as necessary): http://www.thespec.com/opinion-story/4034957-foraging-is-fine-but-not-on-rbg-property/
Garlic Mustard
Some recipes are here: http://the3foragers.blogspot.ca/2014/04/garlic-mustard-recipe-roundup.html
Wood Sorrel (has yellow flowers) - Check out the warnings before you eat this.
Be careful, though! If you cover this topic with your learners, be sure you are providing all the correct and relevant information. Some edible plants may have look alike plants that are poisonous.