01 - In a medium saucepan, combine quinoa, water, and 1/4 teaspoon salt. Bring to a boil, reduce heat to low, cover, and simmer for 15 minutes. Remove from heat and let stand, covered, for 5 minutes. Fluff with a fork and cool to room temperature.
02 - Preheat a grill or grill pan over medium-high heat. Lightly brush plum halves with a little olive oil.
03 - Grill plums, cut side down, for 2–3 minutes until grill marks appear and fruit softens slightly. Remove from heat and let cool. Slice each half into wedges.
04 - In a small bowl, whisk together olive oil, balsamic vinegar, honey or maple syrup, Dijon mustard, rosemary, salt, and pepper to create the dressing.
05 - In a large bowl, combine cooked quinoa, arugula, red onion, almonds, and half of the dressing. Toss gently to combine.
06 - Arrange the salad on a platter or individual plates. Top with grilled plum wedges and sprinkle with goat cheese if using. Drizzle remaining dressing over the salad. Serve immediately.