Preheat the oven to 400°F (200°C).
Prepare the farro according to package instructions until al dente.
Toss the cubed butternut squash with olive oil, salt, and pepper, then spread evenly on a baking sheet.
Roast the butternut squash for 25-30 minutes, or until tender and golden brown, flipping halfway.
In a large bowl, combine cooked farro, roasted squash, chopped kale, red onion, and walnuts.
Make the dressing by whisking olive oil, apple cider vinegar, salt, and pepper in a separate bowl.
Pour the dressing over the salad and toss gently to combine.
Top the salad with crumbled feta just before serving.
Serve warm or at room temperature, garnished with extra walnuts if desired.