After you remove the handles and screws -
Thoroughly clean the entire door on both sides - remove ALL grease, smoke, soot…
Once the door is super-clean, use fine grain sandpaper to remove any existing powdercoat paint. Remove as much as you can.
Using a clean rag soaked in Alcohol or Acetone, clean the door (prep for painting).
Once you are ready to paint, make sure you select a HIGH-TEMPERATURE SPRAY PAINT. Don’t rush spraying the door - it will be a 2 or 3 day process as multiple thin layers of paint are much better than 1 or 2 heavy layers of paint.
FYI - A good black paint that is not too glossy or too flat / matte is Rustoleum blend 241169.