Pulse green tomatoes and jalapeños in a blender or food processor until chopped, leaving small bits.
In a large saucepan, bring tomatoes, jalapeños, and sugar to a boil. Reduce heat to low and add in Jell-O, stirring until dissolved. Simmer (uncovered) for 20 minutes, stirring occasionally. Skim any foam off the top.
Pour into sterilized jars. Let cool on the counter and then refrigerate for up to three weeks.