In a small bowl, whisk together the olive oil, lemon juice, dill, salt, and pepper. Rub the mixture on the salmon fillets and let them marinate in the refrigerator for at least 30 minutes.
Preheat the grill to medium-high heat. Place the salmon on the grill and cook for 4-6 minutes per side, or until cooked through.
In a large bowl, combine the mixed greens, tomatoes, cucumber, and red onion.
To make the vinaigrette, whisk together the olive oil, lemon juice, dill, yogurt, salt, and pepper in a small bowl.
Place the cooked salmon on top of the salad and drizzle with the vinaigrette. Serve immediately.