Remove strawberry hulls, and slice. Add them to a small saucepan, and mix the sugar in well.
Preheat your oven to 400 deg F (204 deg C). Thoroughly wash and dry your glass jars and lids. Set the jars on an oven safe tray (NOT the lids, just the glass jars).
Set the stove to medium heat, bringing the strawberries to a boil, stirring every minute or so to make sure they don't stick or burn at the bottom.
Add the lemon juice and zest, and stir in well.
Meanwhile, "bake" your glass jars in your oven for 20 min to sanitize. I like for these to still be hot when I pour in my jam because it will help them seal. When they are done, use metal tongs to handle the jars - please be careful not to touch them.
Boil until the jam reaches 220 deg F (104 deg C). This can take anywhere from 15-30 min depending on your stove, pan, and the water content of your strawberries. Stay with it! Don't be tempted to raise the heat. :) Once it reaches temperature, remove from heat.
Use clean instruments to pour it into your hot glass jars, and quickly and tightly seal their lids on. Let them cool at room temperature - the metal lids should indent down to indicate they are sealed. My jam lasts months this way (this has been our method for years).