Also, buying garlic-infused olive oil has made life a bit easier (make sure it's the kind without garlic bits in it, Waitrose own brand is a good one) and you can use chives or the green tops of salad onions for an oniony flavour if you need it. Successful meals we've made so far:
Anything that's meat & two veg will work as long as the veg is low-FODMAP
Fried rice
Chicken fajitas with corn tortillas - make sure you don't use a pre-made fajita mix as it likely has onion and garlic powder so I just add smoked paprika, cumin, chili powder and oregano to chicken and peppers and stir-fry, serve with cheese, sour cream, small amount of guacamole, lettuce and chopped tomatoes (not cherry)
Okinawa taco rice (basically a burrito bowl sitting on sushi rice)
Roast chicken with oregano and lemon with roast new potatoes, greek salad on the side (no red onion)
Jacket potatoes with all sorts of toppings, tuna mayo, sour cream/bacon/cheese/chives, etc
Marinated boneless chicken thighs in lime, brown sugar and tamari (no honey)