Step 1

For sauce, in a blender or small food processor combine soaked, drained cashews with the next four ingredients (through garlic). Cover and blend until smooth, gradually adding plant-based milk until sauce is creamy and spreading consistency. Stir in tarragon. Season with pepper.

Step 2

Brush mushrooms with vinegar. Grill mushrooms over medium 15 to 20 minutes or until tender, turning once.

Step 3

Fill buns with spinach, mushrooms, and tomato slices. Spoon sauce over top. Serve immediately.