Rinse fish; pat dry. In a small bowl whisk together the lemon juice, oil, and garlic. Reserve 3 tablespoons of the mixture. Brush remaining lemon juice mixture on fish and the cut sides of the squash. Lightly sprinkle fish and squash with salt and pepper. Grill fish on the lightly greased rack of an uncovered grill directly over medium heat for 8 to 12 minutes or until fish flakes easily when tested with a fork, turning once. During the last 5 to 6 minutes of grilling, grill the squash until just tender, turning once.
Meanwhile, stir basil and mint into the reserved lemon juice mixture.
Transfer the squash to a cutting board; cool slightly and slice 1/8 inch to 1/4 inch thick. Place squash on a serving platter; drizzle with some of the basil mixture. Top with fish; drizzle with the remaining basil mixture. Makes 4 servings.