Preheat oven to 400°F. Place salmon fillets on a baking sheet lined with parchment paper. Stir together lemon juice and mustard in a small bowl; brush evenly over salmon. Use a mini chopper or food processor to chop walnuts. Add breadcrumbs, 1 tablespoon oil, and ¼ teaspoon each salt and pepper, and pulse until blended. Spread nut mixture evenly over salmon, pressing to stick.
Bake 13 to 15 minutes or until salmon is to desired degree of doneness.
While salmon bakes, heat remaining 1 teaspoon oil in a large skillet over medium heat. Add onion, and sauté 5 minutes or until tender. Add garlic and red pepper flakes, and cook 30 seconds longer. Add baby kale, and cook 2 minutes or until wilted, tossing frequently. Stir in chickpeas, tomatoes, lemon zest, and remaining ¼ teaspoon each salt and pepper. Cook 1 minute longer or until thoroughly heated. Serve kale mixture with salmon.