Heat the grill to medium-high heat.
Heat a medium pot over medium heat, add oil and sauté the onions until soft (about 5 minutes).
Add the garlic, cook for an additional minute or two, then add the wine and let reduce until almost dry.
Next, add the coconut milk, poblano and chiles. Bring the pot to a boil, then add 1/2 cup spinach and let cook until wilted (about 1-2 minutes).
Pour the mixture into a blender, add the water and blend until a sauce forms (about 2-3 minutes).
Place the fish on the grill and cook until finished (about 4 minutes per side) season to taste with salt and pepper.
Pour sauce over a bed of remaining spinach with cooked fish.