This unfortunatly was what my gas burner grates looked like. I HATE cleaning them because it litterally takes an hour to make ANY kind of decent headway on getting the gunk off. I saw this tutorial on pintrest and it works! Place 3 TBLS of ammonia (I got a HUGE jug at the dollar store) into a gallon size bag with the grate. Let it sit over night for 12 hours.
In the morning I took the grate out of the bag and used the spray nozzle, from the sink, to get most of it off. It litterally flaked off with the pressure of the hose. The residue that was left I used a green scrubby pad and it mostly came off with one or two swipes of the pad. Only a few spots were stubborn and required elbow grease, but it was about 1/4th of the elbow grease I used when I was just using soap, water and the green scrubby!
This is what 3 TBLS of ammonia after 12 hours looks like!
beautifully clean grate!