Preheat a small dry skillet over medium heat. Add the walnuts and toast, stirring frequently, for 4–6 minutes until fragrant and lightly browned. Transfer to a plate to cool.

Prepare produce

Rinse and dry the mixed greens thoroughly (use a salad spinner or paper towels). Rinse the strawberries, hull and slice them thinly. If using fresh mandarin oranges, peel and separate segments; if using canned, drain well. Thinly slice the red onion if using.

Assemble salad

In a large bowl, combine the dried mixed greens, sliced strawberries, mandarin orange segments, and half of the toasted walnuts. Gently toss to distribute ingredients evenly. If using cheese, sprinkle the crumbled goat cheese or feta over the top and scatter remaining walnuts and red onion slices.

Raspberry Vinaigrette Dressing

Make the vinaigrette: In a blender or food processor, combine the raspberries, white wine vinegar, honey, Dijon mustard, salt, and pepper. Pulse until mostly smooth.

Emulsify: With the blender running on low, slowly pour in the extra-virgin olive oil in a steady stream until the dressing is emulsified. If the dressing is too thick, add water, 1 tablespoon at a time, until you reach a pourable consistency (about 1 tablespoon). Taste and adjust seasoning with additional salt, pepper, or a touch more honey if needed.

Strain (optional): For a smoother dressing, press the vinaigrette through a fine-mesh sieve into a bowl, discarding seeds. Use immediately or refrigerate in a sealed container for up to 3 days. Bring to room temperature and whisk before using.

Dress the salad: Right before serving, drizzle about 3 to 4 tablespoons of dressing over the assembled salad (start with less and add more to taste). Gently toss to coat all ingredients evenly. Serve immediately.