Preheat oven to 400°F (200°C).
Prepare pumpkin: Place pumpkin cubes on a baking sheet, drizzle with 2 tbsp olive oil, and sprinkle with salt and pepper. Toss to coat.
Roast pumpkin: Bake for 25–30 minutes until golden on the edges and soft inside. Let cool slightly.
Toast walnuts: Place walnuts in a dry skillet over medium heat. Stir for 3–5 minutes until fragrant. Remove from heat.
Make dressing: In a small bowl, whisk together olive oil, balsamic vinegar, honey, Dijon mustard, salt, and pepper.
Assemble salad: In a large bowl, add spinach (or arugula), roasted pumpkin, sliced onion, walnuts, and crumbled feta.
Dress it up: Pour the dressing over the salad. Toss gently to combine.
Serve immediately as a main or side dish.