Preheat the oven to 400 degrees F (200 degrees C).
Cut salmon into smaller, equal-sized portions if needed. Pat dry. Season with salt and pepper.
Mix mayonnaise, garlic, dill, and lemon juice together in a bowl. Season with salt.
Place the pecans in a food processor. Pulse for 1 second and check the size of the pieces. You want it to be not quite powdery, but still with some larger chunks. Continue to pulse in 1-second bursts until desired consistency is achieved.
Place the salmon on a baking sheet. Layer the top of the salmon with aioli, then with pecans, until completely covered.
Bake in the preheated oven until fish flakes easily with a fork, 15 to 20 minutes.