Slice the red onions in quarters (remove the skin) and drizzle with the olive oil.
Place cut side up in a small baking dish and roast at 400 degrees Fahrenheit for about 20 minutes or until wilted and slightly caramelized.
Remove the onions from the oven and set aside.
In a large bowl or on a large platter, arrange the arugula, spinach, orange and grapefruit slices (be sure to peel and section the fruit, removing any seeds), the pecans and the goat cheese.
Top with the roasted onions.
For the dressing:
Whisk together all the ingredients for the dressing (or shake together in a mason jar) and pour over the salad just before serving.
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Notes
If you prefer raw onions in your salad, feel free to skip the roasting steps and include the red onions raw and sliced on the salad instead. Roasting mellows their sharp flavour and causes them to taste sweet, which lends to the sweet flavour of this salad.To prepare the salad ahead of time, prepare all the components separately and assemble right before serving for best results.