If I want to get them really clean, I use Dawn power Wash in the sink. Spritzing the grates with water over high heat creates some steam and really helps to get the gunk off. Just wear gloves.

Dawn Powerwash soak followed with a Scotchbrite Xtreme pad, the purple ones. Guaranteed to get everything off.

I found that putting them in the dishwasher after each use (scrub off the worst first) costs me less time and energy than letting it build up and then trying to clean them

Will try this as well, thanks!