Preheat the broiler.
On a broiler pan set 6 inches from the heat, broil the red peppers, turning occasionally, until charred all over 5 to 8 minutes.
Transfer the peppers to a brown paper bag; seal the bag, set it in a bowl, and cool for 10 minutes.
The peppers will steam so that their skins peel off easily.
Meanwhile, lower the oven temperature to 400°F.
Wrap the garlic cloves in aluminum foil and roast until soft about 5 minutes; peel and set aside.
Raise the heat again to broil.
When the peppers are cool enough to handle, peel them over a bowl to catch any juice; discard the stems and seeds.
In an electric blender or food processor, puree the peppers and their juice with the garlic, vinegar, and olive oil.
On a broiler pan rack set 8 inches from the heat, broil the salmon for 2 to 3 minutes; turn and broil another 2 to 3 minutes or until opaque when tested with a fork in the center.
Transfer the salmon to a warm platter and spoon 2 generous tablespoons of the sauce down the center of each fillet, smoothing into a broad ribbon.