Boil reserved snail juices and wine in heavy small saucepan until reduced to 2 tablespoons. Chop parsley, anchovies, garlic and lemon peel together to mix. Combine with snails. (Can be prepared 1 day ahead; refrigerate snail mixture and wine reduction separately.)
Cook pancetta in heavy large skillet over medium heat until golden brown, stirring frequently. Transfer pancetta to plate using slotted spoon. Add oil to skillet and heat. Add walnuts and stir until browned, about 4 minutes. Add snail mixture; stir until hot. Return pancetta to skillet.
Pour in Armagnac and boil until evaporated. Add wine reduction and heat.
Season with salt and pepper. Spoon mixture over croutons and serve immediately.
GARLIC CROUTONS: Brush both sides of bread with oil. Heat heavy skillet over medium heat. Add bread and brown on both sides. Rub both sides of bread with cut side of garlic. Serve warm. Note: Recipe works best with French bread slices that are 1/3-inch thick.