In a small bowl, combine the mayonnaise, mustard, salt and pepper and whisk to combine.
In another bowl, combine the panko breadcrumbs with the rosemary and toss to combine.
Spoon the mayonnaise mixture evenly over the salmon fillets to coat them. Then sprinkle the panko mixture over the salmon and press down firmly with the back of a spoon to adhere the breadcrumbs to the salmon.
Heat the olive oil in a large non-stick skillet over medium. Transfer the fillets to the pan carefully, with the panko side down.
Cook the salmon for 3-4 minutes. Flip over and cook for an additional 3 minutes until desired doneness. Remove from the pan and plate over rice, if desired.
In the same pan used to cook the salmon, add the asparagus, season with salt, pepper and the juice of half a lemon. Cook for 2-3 minutes, stirring occasionally. Serve with the salmon fillets and rice with sliced green onions, if desired.