Dice your oni0on and add it to a skillet over low- med heat with olive oil and salt
Allow your onion to sautee slowly for best flavor, roughly 25 minutes
Once translucent, add coconut aminos, or Worchester sauce, and stir
On a cast iron, melt butter
Assemble your sandwich with pumpkin puree on both slices of bread, cheese, onions, more cheese, then remaining bread
Cook on buttered skillet for a few minutes per side until golden and crisp
Open your sandwich and add arugula, if using
Enjoy!