To cook the salmon: Place the salmon in a shallow dish, sprinkle with 2 tablespoons of sweet balsamic dressing and marinate for 15 minutes.
Preheat the oven to 400 degrees F. Line a baking sheet with parchment paper and lay the salmon fillets on it.
Bake for 10-12 minutes or until just cooked through, but not dry.
While the salmon is cooking, place the potatoes and plantain in a pot with water and cook until tender, drain and reserve.
In a saucepan place the olive oil over medium heat. Add the garlic and cook for 2 minutes. Add the potatoes and plantains to the pot, mash them and mix to combine. Season with salt and pepper, to your taste. Add the scallions for garnish.
Top the salmon with remaining dressing, serve over the mashed sweet potato and plantain.