Season both sides of the fish with salt and pepper. Heat the grapeseed oil in a large 12-inch sauté pan over high heat, until oil starts to shimmer and is very hot. Carefully add each fillet into pan presentation-side down, pressing down on the fish for a few seconds with a spatula to create direct contact with the oil.
Reduce heat to medium-high and cook until fish is golden brown, about 5 minutes; do not move the fish. Carefully flip the fish and reduce heat to medium, and cook until internal temperature reaches 145 degrees, about 7 minutes. During this time, you can tilt the pan and baste the sides of the fish with the hot oil to help with cooking. Turn off the heat and transfer the fish to a paper towel-lined plate to remove some of the excess cooking oil. Drain oil from the pan and return to the stove.
In a medium-size bowl, combine the tomatoes, olives, shallots, garlic, red wine vinegar and 1/4 teaspoon salt. Warm pan over medium heat and add olive oil. When oil is hot, add tomato mixture. Cook until tomatoes are softened and a light sauce forms, about 6 minutes. Add couscous, parsley and basil to pan, and mix to combine. Season with salt and pepper as desired.
Divide tomato basil couscous in 2 bowls and top with halibut. Serve with lemon wedges.