Preheat oven to 425 degrees Fahrenheit.
Line a large baking sheet with parchment paper.
Add green beans to the baking sheet. Toss with the oil, salt and pepper.
Add the salmon to the baking sheet, arranging the green beans around the salmon.
Lightly season salmon with salt and pepper.
Whisk all ingredients for the mustard sauce in a small bowl.
Reserve half of the mustard sauce for serving. Brush the remaining half of the sauce on top of the salmon.
Bake in the oven for 10-15 minutes, until internal temperature of the salmon reaches 145 degrees Fahrenheit.
Check the green beans after 10 minutes. If the green beans are cooked before the salmon, remove from pan and continue cooking the salmon.
Serve salmon topped with the remaining mustard sauce.