main dish to accommodate allium allergy?

A dear friend is allergic to onions, and his wife creatively makes delicious dishes without them, relying instead on celery, carrots and peppers (sweet) as her "Trinity." She also judiciously uses salt and pepper, and various herbs and spices. Her results are always so delicious no one realizes there are no onions.

I wonder if fennel bulb might work as a substitute for onion in some dishes. It's not the same flavor of course, but it might add an analogous sweet and savory flavor. Maybe with a pinch of asafetida as Panfusine suggests added as well, to substitute for that allium bite.

What about a cold soba noodle dish? The sauce could be soy sauce/tamari, toasted sesame oil, a little maple syrup or brown sugar, lime juice and rice vinegar. Add shredded chicken (maybe from a rotisserie chicken to make it easy?), fried tofu cubes, or grilled steak. Mix in some thinly sliced bell peppers, cabbage, carrots and/or bean sprouts for crunch and taste.

Here's another option:
http://smittenkitchen.com/blog/2014/06/pasta-and-fried-zucchini-salad/ --
It's an adaptation of an Ottolenghi recipe that I loved when I tried it.

These are all such creative suggestions. Thanks folks and please keep them coming! There's very little on the internet by way of good recipes that are allium-free, so you are filling a great big gap.

How about honey mustard chicken thighs & breasts or flank steak with a dry rub or roast beef, sliced thin in au jus served with horseradish sauce and small rolls?

I also can't think of anything I make without onion or garlic, but I would look for something with lemon or vinegar or other strong flavor, like ginger. Maybe Rao's lemon chicken omitting the garlic? Also there is a type of Indian cooking that uses no onion or garlic and you can do an internet search, though they are likely vegetarian. Good luck.

A lot of recipes in Indian cuisine catering to orthodox Hindus & Jains completely eliminate alliums, in fact its not allowed at all. The substitute for alliums is asafetida, As much as it stinks to high heaven in its raw form, it blooms into a lovely garlicky aroma when heated. Not sure about how it is used in western recipes though

You could make roasted chicken with lemon and thyme. Typically, I add a head of garlic...just skip that. It will still taste good and that way everyone can eat the same thing. I would cut whole chickens in pieces or buy both light and dark so people have a choice. White wine or sherry and lemon juice added for moistness makes a yummy sauce. Baking lemon wedges with the chicken makes for a tasty and pretty dish. You can use freshly cut lemons and fresh thyme as garnish also.

My concern is that you commonly cook with onions and garlic, so I would use a plate to cut the lemons up and leave the cutting boards in the cabinet. If it's life threatening, then any trace is a danger.

Since this rules out onions, garlic, shallots, scallions, leeks, chives.... why not just cook one of your favorite recipes without the onion or garlic? If it's a pot luck with a pretty large number of dishes, a lot of flavors and tastes will be going on... I wouldn't worry about one of your favorite recipes being allium-less unless it was a key ingredient (like onion soup!).