Wash salmon and pat dry. Heat 1 tablespoon olive oil in a medium skillet; place salmon, skin side up, in pan and sear for 1 minute. Turn fillet over; sprinkle with salt and pepper. Add white wine and garlic to pan; cover and poach until salmon is cooked through, 6–10 minutes.

While salmon is poaching, combine remaining 2 tablespoons olive oil, grapefruit juice, honey, and basil in a small bowl. Whisk to mix well, and season with salt and pepper. Combine salad greens and arugula in a large bowl and toss with just enough dressing to lightly coat leaves.

Divide salad among four plates. Top each with 1/4 of the cooked salmon. Arrange avocado slices and blackberries on top of each salad. Sprinkle with walnuts and drizzle lightly with additional dressing. Serve immediately.