Place water in a small saucepan and sprinkle gelatin over water. Place pan over low heat and stir constantly until gelatin dissolves, about 3 minutes. Set aside.
Melt butter in a large skillet over medium heat; add onion and mushrooms and cook about 4 minutes. Place mixture in the bowl of a food processor; add gelatin and remaining ingredients and process until pureed. Pour into a 3-cup mold and chill until firm. Unmold and serve with crackers.
Makes 8 servings.
This vegetable pâté has a lively flavor and texture, but is surprisingly low in calories.