It’s good to see you back again.
Unfortunately, I don’t know of any material for teaching chefs; I guess you’re going to have to design the course yourself.
It might help if you find out whether the chefs will be reading recipes in English or whether they’ll be speaking to other chefs. Then you’ll know whether to focus on spoken or written language. Bear in mind that the vocabulary of cooking can be difficult: roast, dice, chop, baste.... However, the structures of recipes are fairly straightforward, instructions and sequencers: next, then you fry the bacon with the onions..... In some ways it’s easy for beginners and in other senses a real challenge for them.
There’s no way around it, the vocabulary is complicated and I suggest you use a higher level book for that aspect. Take a look at English Vocabulary in Use (Cambridge University Press) levels intermediate and pre-intermediate; I’m sure they contain language linked to cooking. You’ll be able to use the units as they are to teach the language and then you might need to adapt the practice activities. You could also use images from a picture dictionary, but only if you think your students won’t find it childish.
You can take recipes and jumble up the words within sentences and sentences within the recipe and ask students to re-order them to practise the language. The ultimate would be getting them into a kitchen and using the language to tell you how to cook – what an experience!!
I also saw an activity in ESP Ideas (Longman). The teacher reads out a recipe as a dictation. Ask students to read the dictation back to you and correct any language errors. Do some work on the format and style of the recipe; then ask students to use the model to write a recipe. Students then read each others' recipes and comment and/or correct. You might like to spread this activity out over 2 lessons as it is rather long.
Those are the ideas I have for the moment; if I think of any more, I’ll add them to this post and let you know.