In a small bowl toss the potatoes with half of the olive oil and season with salt and pepper.
In another small bowl, dress the green beans with the rest of the olive oil and mustard and season to taste with salt and pepper.
Line a sheet pan or lipped jelly roll pan with parchment paper or foil.
Place the potatoes on one side in an even layer, and repeat with the dressed green beans.
Place the 4 fillets on the tray and spread the tapenade evenly on the top of the cod. Scatter the grape tomatoes on the pan.
Bake until fish flakes easily with a fork and potatoes are tender, about 15-20 minutes. Garnish or serve with the lemon and parsley if desired.