Trim each lemongrass stalk to about 10cm long, then slice each stalk in half lengthwise to create 8 x 10cm skewers.
To make the marinade, combine all ingredients in a large bowl. Check for seasoning.
Cut salmon into 24 equal-sized cubes and add to the marinade. Toss well to combine and cover with plastic wrap. Set aside for 30 minutes.
Thread three pieces of salmon onto each piece of lemongrass to make 8 skewers.
Heat an oiled barbecue or char-grill plate to medium high and cook skewers for about a minute on each of 4 the sides, until nicely charred.
Pile onto a platter and nestle the cucumber alongside the skewers. Then scatter fresh mint and crispy shallots over the top and serve with lime wedges on the side.