Four of these omega-3-packed bites served over grains makes a great supper.
1. Purée 1 cup walnuts with parsley and garlic in food processor until thick and pasty. Add lentils, 2 tsp. vinegar, sage, and walnut oil; purée until smooth. Season with salt and pepper, if desired.
2. Fill each mushroom cap with 11/2 Tbs. walnut mixture, and press remaining walnut halves into filling. Place on plate.
3. Heat olive oil in large skillet over medium-high heat. Add mushrooms, round side down, and cook 5 minutes, or until mushrooms begin to release their juices and brown on bottom, shaking pan occasionally. Carefully add broth to pan, cover, and reduce heat to medium-low. Simmer 10 to 15 minutes, or until mushrooms are tender and filling has puffed and browned slightly. Remove mushrooms from pan, then add remaining 2 tsp. vinegar to pan. Simmer 1 to 2 minutes, or until sauce thickens slightly. Serve mushrooms drizzled with sauce.