Preheat broiler with rack in the highest position.
In a fry pan, soften onions and garlic in olive oil for about 2 minutes. Add
balsamic vinegar. Set aside.
Slice pork diagonally against the grain into very thin slices.
Slice baguette diagonally into 1/2–inch slices. Spread 1/2 tsp mustard on each slice, then 2 pork slices. Follow with some onion mixture and then fig slices. Top with cheese and lastly nuts.
Drizzle each crostini with a bit of olive oil and broil just a few minutes to melt cheese – keep watching so not to burn.