Pour three ounces pineapple juice into each glass.
Top up each glass with champagne. Serve cold.
Notes
Want jalapeño flavor with less heat? Remove the seeds from the jalapeño slices.For a spicier pineapple mimosa, muddle the jalapeño slices to release more of the oils, juices, and heat. You can also up the spice level by letting the jalapeño "steep" in pineapple juice for a while (about an hour or so) before adding champagne and serving.