6 thick, woody branches rosemary
18 large or 30 medium raw shrimp, shelled and deveined
1/4 cup liquid tamarind concentrate, or 1 tablespoon tamarind paste mashed with 3 tablespoons hot water
1/4 cup orange marmalade
1/4 cup olive oil
1/8 teaspoon salt
Freshly ground pepper
1 bunch arugula

Pick off the rosemary leaves near the base of each branch.  To skewer the shrimp, place shrimp flat on their sides on a cutting board so that they look like letter Cs.  Insert a rosemary branch through the tail end of the first shrimp (the bottom of the ÒCÓ) and push it through to pierce the head end (the top of the ÒCÓ).  Continue skewering the shrimp, dividing them evenly between the skewers.  Place skewers in a baking dish or on a large plate.
Place tamarind concentrate or softened paste in a small bowl.  Add orange marmalade and olive oil and stir to combine.  Brush skewered shrimp with mixture.  Cover with plastic and refrigerate 15 minutes.
Light a grill or preheat a grill pan over high heat.  Season marinated shrimp with salt and pepper.  Place as many skewers as will fit on grill.  Cook until shrimp are firm to the touch and opaque, about 2 to 3 minutes per side.  Repeat with remaining skewers. 
Spread arugula over a large serving dish.  Arrange shrimp skewers over arugula.  Serve immediately.