Preheat the oven to 350 degrees with rack in center. Spread nuts on a rimmed baking sheet, and toast them in the oven until they are fragrant, about 8 minutes. Transfer nuts to a clean kitchen towel, and rub nuts in towel vigorously between your hands to remove the brown skins. Lightly brush an 8-by-12-inch rimmed baking pan with the oil. Spread the peeled nuts in the pan.
In a medium saucepan, combine sugar and lemon juice. Cook over medium heat, brushing down sides of pan with a damp pastry brush to remove any sugar crystals that may form, until mixture is amber, about 9 minutes; do not stir. (Pan may be swirled gently about halfway through to incorporate any uncooked sugar.) Pour directly over nuts to create a thin layer. Set aside to cool, at least 30 minutes.
Place half the praline in the bowl of a food processor; process until the praline is very fine with no sharp pieces. Cut the remaining praline into small pieces for decoration.
Store any leftover praline in an airtight container. Don't let pieces overlap much or they will stick together. Keep at room temperature for up to one week; use as a topping for desserts or ice cream.