Pour water into pressure cooker and add lemon peel, brown sugar, and salt. Stir in sweet potatoes. Secure lid. Over high heat, develop steam to high pressure. Reduce heat to maintain pressure and cook 4 minutes.
Release pressure according to manufacturer's instructions. Remove lid. Transfer sweet potatoes to a serving dish with a slotted spoon. In a skillet, melt butter; heat until bubbly. Stir in pecans.
Add syrup and cornstarch, stirring to blend. Add to liquid in cooker and cook over med. heat until thickened. Spoon over sweet potatoes. Garnish with whole pecans.