1/2 small shallot, peeled, very finely chopped 2 tablespoons fresh lemon juice 1 to 2 teaspoons Dijon mustard 1/2 teaspoon honey Kosher salt and freshly ground black pepper 1/4 cup olive oil 1/4 cup vegetable oil 2 tablespoons capers, drained, rinsed, patted dry Preheat the oven to 250 degrees. Brush a large baking dish with a bit of oil.
In a medium bowl, combine chickpeas, cumin and 1 tablespoon oil. Mash about half of chickpeas in the bowl with a fork; season all with salt and pepper. Transfer chickpea mixture to prepared dish.
In a large skillet, heat remaining 1 tablespoon oil over medium heat. Add the garlic and cook, stirring, until fragrant, about 30 seconds. Add the mustard greens or rainbow chard and cook, tossing, until slightly wilted, about 1 minute. Add honey and water; season with salt and pepper. Cook, tossing, until greens are completely wilted, about 2 minutes more. Transfer to baking dish, placing the greens on top of the chickpea mixture.
Generously season each salmon fillet with salt and pepper; arrange on top of the greens and chickpea mixture and drizzle with oil. Bake until salmon is opaque in the center, 25-30 minutes depending on its thickness.
Meanwhile, make the vinaigrette. In a small bowl, whisk shallot, lemon juice, mustard and honey; season with salt and pepper. Gradually whisk in olive oil; season with salt and pepper.
Heat vegetable oil in a small saucepan over medium-high heat. Cook capers until opened and crisp, about 30 seconds; drain on paper towels.
Drizzle salmon with vinaigrette and top with capers.