Bring a small pot of water to a boil, and then remove it from the heat.
Add the cashews and let them soak in the hot water for 30 to 40 minutes.
Drain the cashews and place them in a blender.
Add the garlic, lemon juice, Dijon, capers, onion powder, salt, black pepper, and water to the blender.
Blend until smooth, scraping down the sides of the blender if necessary. You can add more water 1 tablespoon at a time if you prefer a thinner dressing. Taste and adjust for salt or other seasonings.
Serve the dressing immediately over Romaine lettuce and croutons, or refrigerate for up to 1 week to serve later.