Combine the lentils, bay leaf, garlic, onion, oil, and water in the cooker. Lock the lid in place and over high heat bring to high pressure. Adjust the heat to maintain high pressure and cook for 7 minutes. Reduce pressure with a quick-release method. Remove the lid, tilting it away from you to allow any excess steam to escape.
If the lentils are not done, lock the lid back in place and return to high pressure for a minute or two. Remove the bay leaf. If using as a side dish, drain off most of the cooking liquid. Stir in mustard, parsley, and salt. Adjust seasonings and serve.
Serves 6.