Dissolve the sugar in the boiling water. Simmer for 5 minutes, without stirring.
Remove the syrup from the heat, pour it into a bowl, and set in the refrigerator to cool.
Place the frozen strawberries in a food processor. Process until fairly smooth, but not puréed.
Add the syrup and lemon juice, and pulse briefly, just to combine.
Place the mixture in a shallow pan. Place the pan in the freezer.
After 2 hours, use a fork or spoon to stir it around, bringing the frozen edges into the center. Return to the freezer.
Continue to stir every hour or so, until the sorbet is nearly as firm as you like. This may be as little as 4 hours total, start to finish; or it may take longer, depending on the temperature of your freezer.