If you would like to avoid a burning sensation on your hands or fingers, wear gloves when handling jalapeños. If you don't have gloves, hold the jalapeño with a damp paper towel.
Slices
Trim off the stem.
Use a paring knife and/or spoon to remove the membrane and seeds from inside the pepper.
Cut the pepper crosswise into slices of your desired size.
Diced
Trim off the stem and cut the pepper in half lengthwise.
Use a paring knife and/or spoon to remove the membrane and seeds from each half.
Cut each half lengthwise into thin strips.
Cut the strips crosswise into pieces.
For poppers
Keep the stem on the pepper. Cut in half lengthwise.
Use a paring knife and/or spoon to remove the membrane and seeds from each half.
Video
Notes
If you cut jalapeños without gloves or a paper towel and have a burning sensation on your hands, try rubbing them with a little bit of olive oil. Keep the oil on your hands for a minute then wash with soap and water.
Store cut jalapeños in an airtight container in the fridge for up to 5 days.