Preheat your oven to 400°F (200°C). Place the salmon fillets on a baking sheet lined with parchment paper. Season with salt and pepper.
Bake the salmon in the preheated oven for about 10 minutes, or until it flakes easily with a fork. Alternatively, grill the salmon in a non-stick skillet or grill pan over medium-high heat for about 5 minutes on each side.
While the salmon is cooking, prepare the salad. In a mixing bowl, combine the mixed greens, cherry tomatoes, cucumber, and red onion.
In another small bowl, whisk together the olive oil, lemon juice, Dijon mustard, salt, and pepper to create the dressing.
Slice the avocados in half, remove the pit, and carefully scoop out the flesh. Cut the avocado into cubes.
Once the salmon is cooked, let it cool slightly before breaking it into bite-sized pieces.
Gently toss the salad mixture with the dressing. Plate the salad and top with avocado cubes and pieces of salmon.
Garnish with fresh dill or parsley if desired.