Place bacon in a large, deep skillet. Cook over medium high heat until evenly brown. Drain, crumble and set aside.
Place vinegar, sugar, red onion, mustard powder, and salt into the bowl of a blender. Cover, and puree on high until smooth. Reduce blender speed to medium-low; slowly pour in the vegetable oil and blend until incorporated and the dressing is creamy. Stir in the poppy seeds and set aside.
To serve, toss the romaine in a large bowl with the crumbled bacon, Mandarin oranges, and enough dressing to moisten. Place onto salad plates and sprinkle with toasted almonds.
