Pat the salmon fillets dry with paper towels and brush them with 1 tablespoon of olive oil. Season generously with dried oregano, salt, and black pepper on both sides.

Heat a grill pan or non-stick skillet over medium-high heat. Once hot, add the salmon fillets skin-side down and cook for 4-5 minutes until the skin is crispy.

Flip the salmon carefully and cook for another 2-4 minutes, or until the fish is opaque and flakes easily with a fork. Remove from heat and let it rest for a few minutes.

While the salmon rests, whisk together the extra virgin olive oil, fresh lemon juice, Dijon mustard, salt, and pepper in a small bowl until emulsified.

In a large salad bowl, combine the mixed greens, halved cherry tomatoes, sliced cucumber, and red onion. Drizzle half the dressing over the greens and toss to coat.

Divide the salad onto two plates, top with the sliced avocado and the warm grilled salmon fillets. Drizzle the remaining dressing over the fish and avocado before serving immediately.