This recipe can be prepared in 45 minutes or less.
Cut bacon into 1/2-inch pieces and in a large heavy skillet cook over moderate heat, stirring, until crisp and golden. With a slotted spoon transfer bacon to paper towels to drain.
Thinly slice cabbage and discard coarse stems from mustard greens. In a large steamer rack set over boiling water steam cabbage, covered, until crisp-tender, about 10 minutes. Transfer cabbage to a large bowl and keep warm, covered. In steamer rack set over boiling water steam mustard greens until tender, 10 to 15 minutes. Add mustard greens to cabbage and keep warm, covered.
Mince garlic. In a small saucepan heat garlic, butter, and oil until butter is just melted. Drizzle butter mixture over vegetables, tossing to distribute evenly, and season with salt and pepper.
Transfer vegetables to a serving dish and serve topped with bacon.