1. In a large salad bowl, place spinach, carrots, oranges, fennel, and scallions.
2. In a small bowl, mix vinegar, shallots, mayonnaise, mustard, miso, orange zest, and salt. Whisk until mixture is milky and no lumps remain. Slowly drizzle both oils into mixture, whisking until emulsified and slightly thickened.
3. Pour dressing over salad ingredients. Toss, sprinkle with sesame seeds and serve immediately.