Small touches like the charred lemon vinaigrette and tart pomegranate arils elevate this speedy salad into a showstopping main dish. Preheat your sheet pan to get a jump-start on cooking the squash and onions.
Place a baking sheet on rack in upper third of oven; preheat broiler to high. Once hot, carefully remove baking sheet from oven; place squash, onion, and lemon (cut side down) on baking sheet. Broil until charred, 7 to 8 minutes. Let cool; squeeze juice from lemon halves into a small bowl.
Whisk together olive oil, vinegar, maple syrup, mustard, orange zest, 1 teaspoon lemon juice, 1/2 teaspoon pepper, and 1/4 teaspoon salt in a medium bowl; set aside.
Heat canola oil in a large nonstick skillet over medium-high. Sprinkle salmon flesh with remaining 1/4 teaspoon pepper and remaining 5/8 teaspoon salt. Cook salmon, skin side down, until skin is crisp, 3 to 4 minutes. Flip fillets; cook 2 to 3 minutes.
Place kale, spinach, pomegranate arils, squash, and onion in a large bowl. Add vinaigrette; toss to coat. Divide salad and salmon among 4 bowls; spoon 1/2 teaspoon lemon juice over each fillet.