Tofu with Scallions

1 package firm tofu
1 bunch scallions
2 tablespoons peanut or vegetable oil
2 to 3 tablespoons oyster sauce

Drain the tofu well in paper towels, then slice 1/4 inch thick. Keeping white and green parts separate, cut the scallions into 1/2- to 1-inch pieces. Heat oil in a wok or heavy skillet. Over high heat, saut