Mix oil, lemon juice, worcestershire sauce, and curry powder in small bowl. Brush tofu cubes with marinade and place in a container with a lid. Refrigerate for about one hour.
Preheat Oven to 350 degrees F.
Peel and cut yam into 1/2 inch cubes and place on a cooking sheet covered with tinfoil. Sprinkle with 1 tablespoon vegetable oil, and 1 tablespoon curry powder. Bake in oven for 20min, or until tender.
Sautee onions in butter and 1 teaspoon curry powder. Add marinated tofu and fry about 5min.
Then add yams and fry another 5min. Add coconut milk and cornstarch, and let simmer about 10min.
Sprinkle 1 tablespoon curry powder and stir in right before serving.