Using a vegetable peeler, slice the carrots lengthwise into thin ribbons. Thinly slice the red onion and finely chop the fresh dill.
Toast the walnuts in a dry pan over medium heat for 2-3 minutes until fragrant and lightly golden. Let them cool, then roughly chop.
Cut the feta into small, bite-sized cubes and set aside.
In a small bowl, whisk together olive oil, orange juice, grainy mustard, honey, salt, pepper, and chili flakes until smooth.
In a large bowl, combine the carrot ribbons, red onion, feta cubes, toasted walnuts, and chopped dill. Drizzle the dressing over the salad and toss gently until everything is evenly coated.
Serve immediately as a fresh, light salad.
Notes
This salad is best served fresh.
Store dressing separately and add feta and walnuts before serving if making ahead.