Break broccoli into florets. Cut stalk into thin strips, or discard stalk. Roughly dice the florets.
Lay broccoli and diced onion on a single layer on a baking sheet. Drizzle with olive oil, and then sprinkle with salt and red pepper flakes.
Roast 9-10 minutes, or until the broccoli is tender.
While the broccoli roasts, whisk together all vinaigrette ingredients.
Add roasted broccoli and onion to a bowl, along with the raisins and almonds. Toss with the vinaigrette, and serve.
Make Ahead: Assemble the salad without the dressing up to 1 day ahead, and store in the refrigerator. Toss with the dressing right before serving. Serve cold.