Heat the olive oil in a skillet over medium-high heat, then saute the onion, garlic, and jalapeno until softened, about 5 minutes. (Tip: Add in a few of the jalapeno seeds if you want a spicier dip.)
In a blender, add in the drained beans, cumin, salt, lime juice, and water. Add in the sauteed vegetables, then blend. Stop and scrape down the sides of the blender, and blend until the dip is very smooth.
You can serve the dip right away, or you can transfer it to a storage container with a lid (this makes about 1 1/2 cups) and store it in the fridge to chill. The flavors will meld and mellow slightly as the dip cools, and it will thicken up in texture.
You can store this dip in the fridge for up to a week.
When working with fresh jalapenos, be sure to avoid touching their seeds and juices as much as possible. They can burn your skin! Definitely avoid touching your eyes or face, and wash your hands as soon as possible to avoid any burns from the juice.