First, to save time, wash the potatoes and, without drying them, place them in a glass bowl covered with plastic wrap. Poke a couple of holes to let the steam escape and microwave for 10 minutes. Afterward, check if the potatoes are soft by poking them. Once soft, place them on a plate to cool, then peel and cut them. Set aside.

In a blender, combine all the ingredients for the aioli: the sliced garlic, the egg (which should be at room temperature), and salt. Gradually add oil until you achieve a mayonnaise-like texture, but it should be more like a cream.

Turn on the oven broiler. While it heats up, slice the peeled potatoes into half-inch slices. Use them as a base along with the green pepper, place the cod loin on top, and cover with a generous layer of aioli. Put it in the oven, keeping an eye on the cod as it gratinates quickly. Once done, add the sauce to the plate and serve.