I've just been on the official site and read the onion page. As far as I can see roast onions are fine.
Taken from Dr D himself.........
In France, it is difficult for a cook to work without using any garlic, onions, salt or pepper. Once the onion has been cooked enough to get rid of its sulphur, (this is what stings makes you cry and makes your breath smelly), they can actually be mild, even sweet with a caramelized flavor. By cooking onions slowly over gentle heat you can transform them into onion confit and for that matter, you may as well go ahead and make onion marmelade. It's the onion's sweetness that is so useful, especially for anyone dieting who is tortured by not having any sugar. This sweet taste comes from the fructose which has a sweetening ability more powerful than that of sugar.
And the most important part "Onions can be also be cooked in the oven,"
Roast away Sid!!x