Combine mustard, mayonnaise, salt, and pepper in a bowl. Slather this mixture on the top of each salmon fillet. Using the Dijon mixture to adhere, layer radish slices on top in a geometric pattern.
Heat oil in a saute pan. Cook salmon, radish-side down until they are browned and fish is nearly cooked through, approximately three minutes. Flip and cooked for another two minutes; remove from pan.
Garnish with microgreens and fennel pollen.