Preheat oven to 450F. Line a baking sheet with parchment paper.
Place the salmon, skin side down on the parchment line baking sheet.
In a small bowl, whisk the mustard, honey and vinegar together.
Using a pastry brush, evenly brush the mixture over the top of the salmon.
In a medium bowl, toss the potatoes with half of the olive oil, salt and pepper. Repeat with the green beans.
Place the green beans on one side of the salmon and the potatoes on the other.
Place lemon slices on top of the salmon. Sprinkle with thyme and additional salt and pepper if desired.
Bake for 20 to 26 minutes or until the internal temperature reaches your desired doneness. (125F = medium, 140F = fully cooked). Don't have a thermometer? The salmon is done within a few minutes of the top no longer being shiny and it appearing opaque.
Let rest 5 minutes before serving.