Make the couscous according to the package directions and keep warm.
Meanwhile, score the bass skin by penetrating it only slightly with a sharp knife and creating a 1 1/2-inch-long slit in each fillet.
Heat a large nonstick skillet over high heat for 1 minute.
Meanwhile, sprinkle the fillets with the juice of 1 lemon, then season with salt and pepper.
Add the butter to the skillet and let melt. Add the fish skin-side down and gently press the center of the flesh on each fillet for about 10 seconds to ensure that the skin stays flat and can get crispy.
Reduce the heat to medium. Add the shallots, capers and garlic around the fish and cook, spooning the butter over the fish, until the fish is cooked through, about 3 minutes.
Transfer the fish, skin-side up, to a plate and remove the skillet from the heat. Add the couscous, cucumbers, tomatoes, onions, parsley and the remaining juice of 1/2 lemon to the skillet and toss to coat and combine.
Serve the couscous salad on plates and top each with 2 fish fillets. Enjoy!