Just some "tile over metal ideas" I've picked up over the years. You'll have to decide how you want to do it. I have found all have worked well for anchoring tile to metal. Just rough up the powder coat first.
Drill lots of 1/4" holes into the metal so the thinset will squeeze through and anchor the tile into place when it dries. Very strong bond.
Spot weld wire lathe to metal. Skim off with thinset and tile.
Use epoxy thinset. Check the heat specs.
Use silicone rubber. Dries quick and sticks well but you'll have to check the heat specs.
By the way, don't grout around the inside lip of your heatilator face- use caulk.