1. Fill a large bowl halfway with ice cubes and add some cold water. Place a colander squarely inside the ice bath. The colander will keep you from having to pick the asparagus out from amongst the ice cubes in the ice bath.
2. Bring a large pot of water to a rolling boil. Add 1 teaspoon salt. Add the asparagus and cook for 1 to 1½ minutes. You want them to be crunchy. If the asparagus are thicker, cook for 1½ to 2 minutes.
3. Remove the asparagus from the water using a slotted spoon and transfer them to the colander inside the ice bath. Move them around gently so the ice water penetrates the asparagus and accelerates the cooling process. Vegetables take longer than you think to cool so allow them to sit a few minutes in the ice water. Hold a piece of the asparagus in your hand for a few seconds to assure that it's really cool (even in the center). If the piece still feels warm, allow them to cool longer in the ice bath. Place them on a kitchen towel to drain any excess moisture.
4. Heat oil a medium skillet until hot (but not smoking), add the walnuts and season with 1/4 teaspoon salt. They should bubble and fry slightly in the oil. When you can smell the walnuts, add the paprika and cayenne and lower the heat to medium. Cook for about 30 seconds, stirring constantly, and transfer the mixture to a bowl. Set aside.
5. Toss the asparagus in the bowl with the walnuts and the oil. Let this mixture sit in the refrigerator for a few hours or a few minutes. When ready to serve, stir in the lemon juice. Serve immediately.