Preheat the oven to 400°F and line a baking sheet with parchment paper.
In a small bowl, combine olive oil, Dijon mustard, lemon juice, parsley, dill, chives, garlic powder, salt, and black pepper to form a smooth herb paste.
Place salmon fillets on the prepared baking sheet and spread the herb paste evenly over each fillet.
Bake the salmon for 12 to 15 minutes until cooked through and flaky.
In a large bowl, toss salad greens, cherry tomatoes, cucumber, red onion, nuts, and feta cheese, if using.
Whisk together extra-virgin olive oil, white wine vinegar or lemon juice, honey or maple syrup, Dijon mustard, salt, and pepper in a small bowl to create the vinaigrette.
Drizzle the vinaigrette over the salad and toss gently to coat.
Divide the salad among four plates and top each with a warm herb-crusted salmon fillet. Serve immediately.