Preparation Preheat broiler. Make several diagonal slashes (1/8 inch deep) in mackerel skin about 1 inch apart. Coat both sides of mackerel with 2 tablespoons oil, then season with 3/4 teaspoon salt (total). Broil mackerel, skin side up, in a 4-sided sheet pan about 4 inches from heat until just cooked through and skin is crisp in spots, about 7 minutes. Meanwhile, whisk together remaining 1/3 cup oil, lemon juice, mustard, 1/4 teaspoon salt, and 1/8 teaspoon pepper in a large bowl. Reserve 2 tablespoons vinaigrette, then toss radicchio and parsley with remaining vinaigrette. Serve salad topped with avocado and mackerel and drizzled with reserved vinaigrette.
Preparation Preheat broiler. Make several diagonal slashes (1/8 inch deep) in mackerel skin about 1 inch apart. Coat both sides of mackerel with 2 tablespoons oil, then season with 3/4 teaspoon salt (total). Broil mackerel, skin side up, in a 4-sided sheet pan about 4 inches from heat until just cooked through and skin is crisp in spots, about 7 minutes. Meanwhile, whisk together remaining 1/3 cup oil, lemon juice, mustard, 1/4 teaspoon salt, and 1/8 teaspoon pepper in a large bowl. Reserve 2 tablespoons vinaigrette, then toss radicchio and parsley with remaining vinaigrette. Serve salad topped with avocado and mackerel and drizzled with reserved vinaigrette.