Line a full-size sheet pan with parchment paper. Place a wire cooling rack over the sheet pan and spray it with nonstick cooking spray. Place the sheet pan near a marble surface. Have 3 pairs of latex gloves available.
Place the sugar in a saucepan with about one-quarter of its weight in water or enough to obtain a wet-sand texture. Add the lemon juice to prevent crystallization. Make sure there are no sugar crystals along the inside of the pot and that all the sugar has been hydrated. Begin cooking the sugar over high heat.
Toast the seeds until they begin to have a toasted aroma and a light brown color in a 160°C / 325°F oven for about 6 minutes. If the sugar has not caramelized by this point, keep the seeds hot until it does. They can be kept in the oven, but turn it off and open the oven door slightly. If cold seeds are added to the sugar, it will crystallize.
Cook the sugar over high heat until it reaches 170°C / 338°F. Turn the heat down to low and stir in the toasted seeds. Make sure all the seeds are coated in sugar and continue to stir until you start hearing a popping sound, about 45 seconds, then pour the contents of the pot over the greased wire rack.
Put on the 3 pairs of gloves and spray nonstick cooking spray on them. Working very quickly, separate the seeds from each other and immediately place them on the marble to cool quickly.
Reserve in an airtight container at room temperature. If kept in a dry environment, they will keep for 1 week.