I love mashed cauliflower. I mash it with cream cheese for a creamier texture.
I also love it roasted. Sliced thin then roasted until it turns dark brown around the edges... the two of us can wipe out a whole head in one sitting.
Brussel sprouts and asparagus and eggplant are also fabulous roasted. Just a bit of oil and some s&p is all they need.
There are lots of your regular recipes that can easily be low carb. Roast chicken, any stir-fry, most any curry (without potatoes), any piece of meat or seafood, salads. Generally speaking, where you'll find the hidden carbs is in the sauces. BBQ sauce and ketchup, a lot of salad dressings, have TONS of carbs. Learn to use mayo and mustard instead (read the labels of both though, some are not so good), or experiment with making your own.
To give you an idea, some favorites around here, when we first started Atkins:
Buffalo Wings with homemade blue cheese dressing and raw broccoli
Sloppy Joes or Chili w/o beans (I think I've posted both these recipes here)
Hamburger salad (I still have this once a week... a bacon cheeseburger with all the trimmings on a bed of lettuce instead of a bun)
Cream of soups (crab, clam, mushroom, broccoli, asparagus, tomato, etc.)
Jalapeno Poppers (jalapenos stuffed with flavored cream cheese, wrapped in bacon and broiled)
Meatballs and spaghetti squash
Meatloaf and mashed cauliflower
Once you get the hang of it, you'll discover that with minor changes, a lot of recipes are still useable (I'm not talking about baked goods recipes, though).
If you'd like the recipes for any of the above, let me know. I even have 3 recipes for crackers.
Something to think about though is what he's going to do for sweet. I don't know anyone that can cut everything sweet out of their life and stick to it. Whether you use Xylitol or honey or applesauce or stevia, etc. is up to you.
I do have some LC recipes for desserts, once you've decided on a source of sweet... custards, cheesecakes, pound cake (made with almond flour), etc. Let me know if you want recipes.