Toast the nuts: Spread the pecans or walnuts on a baking sheet and toast in a 350°F (175°C) oven for 5-7 minutes, or until fragrant and lightly golden.
Make the dressing: In a small bowl, whisk together olive oil, balsamic vinegar, Dijon mustard, honey, salt, and pepper.
Assemble the salad: In a large bowl or on a platter, combine the fresh greens, pomegranate seeds, orange segments, toasted nuts, and red onion.
Dress the salad: Drizzle the dressing over the salad and toss gently to combine. Add crumbled feta or goat cheese, if desired.