Make the vinaigrette. In a small container, combine the shallots, lemon juice, rice vinegar, olive oil, salt and pepper. Shake to blend.

Place the arugula in a large serving bowl with the onion. Peel the oranges, and use a paring knife to remove all of the white pith from the outside of the fruit. Cut the oranges crosswise into slices, and cut those slices into 4 pieces. Add these to the bowl. Pour the dressing on the salad, and toss to combine. Scatter the pomegranate seeds over the top and serve.