Spread vegan butter on one side of each bread slice.
Heat a skillet on medium heat.
Place one slice of bread, buttered side down, on the skillet.
Layer with vegan cheese, vegan ham, and a hint of mustard.
Top with another bread slice, buttered side up.
Grill until the bottom turns golden brown, about 3–4 minutes.
Flip and toast the other side until the cheese melts and bread crisps.
Remove from heat, slice diagonally (obviously), and serve hot.