Place the first 7 ingredients in food processor and puree. Transfer this mixture to a small pot and simmer 3 to 4 minutes, until lightly thickened. Season with salt, and then cool to room temperature. Cover and chill the sauce in the fridge until needed.
Preheat an indoor or outdoor grill to medium-high. Brush the prawn kebabs with the oil; season with salt and pepper. Grill the kebabs 1 to 2 minutes per side, or until just cooked through and bright pink. Place 2 kebabs on each of 4 plates and place a bowl of the sauce alongside for dipping.
Note: To peel the peaches, cut a small star into the blossom end. Plunge the peaches into boiling water for 1 to 2 minutes. Cool in cold water and slip off the skins.