In a small dry skillet over medium heat, toast sesame seeds for 1-2 minutes, stirring frequently, until golden and fragrant. Remove from heat and set aside to cool.

In a medium bowl, whisk together lemon juice, garlic, mustard, honey, salt, and pepper. Gradually drizzle in olive oil while whisking constantly to emulsify. Stir in the toasted sesame seeds. Drizzle a tablespoon of the dressing over the salmon, using your hands to gently coat all sides. Place the remaining dressing into the refrigerator to chill while preparing the salmon and the salad.

In a medium skillet over medium heat, add olive oil. Once hot, add salmon and sear for about 3-4 minutes. Flip and repeat on the other side, until cooked through (about 3-4 more minutes), for a total of 6-8 minutes. Salmon should reach an internal temperature of 145°F. Remove the salmon from the skillet and let it rest for a few minutes before cutting it into bite-sized pieces.

In a large bowl, combine lettuce, cucumber, tomatoes, and onion. Add the cooked salmon on top (warm or cold). Drizzle with the remaining dressing before serving.