Preheat the oven to 360 F. Jalapenos can be baked whole or cut into halves. To make the pepper less spicy, you can remove the seeds. It is best to do this with latex gloves.
Cover the baking sheet with parchment and grease it with olive oil. Lay out the halves or whole peppers with the stalks cut off. Brush or spray oil on the outsides.
Sprinkle salt on all of them and bake for 10 minutes for soft brown charred skins on the peppers or 7 minutes for firmer, greener peppers.
Pour peppers into a paper bag when done ideally, fold closed and let them sit this way for 15 minutes to separate the skins from the flesh even easier.
Peel the finished pepper dice fine and use immediately after roasting.