In a medium mixing bowl, whisk the pineapple, soy sauce, agave syrup, ground ginger, and minced garlic
Pour half into a container to reserve and then place the salmon in a bag with the marinade, turning to coat
Refrigerate for at least 30 minutes, up to overnight
Set the oven broiler to high
Place the marinated salmon on a foil-lined baking dish and spoon some of the pineapple from the marinade onto the salmon then discard the remaining marinade
Broil for about 20-25 minutes, until the salmon is cooked through (this will vary based on the thickness of the salmon)
While the salmon is cooking, heat the reserved teriyaki sauce in a small saucepan over medium heat
Simmer for about 3-5 minutes, until slightly thickened
Pour the teriyaki sauce over cooked salmon and serve immediately