Mix dill, green onions, pistachios, and 1/4 cup oil in medium bowl. Season to taste with salt and pepper. DO AHEAD: Pistou can be made 2 hours ahead. Let stand at room temperature.
Heat 1/2 tablespoon oil in heavy large skillet over medium-high heat. Add peppers and sauté until beginning to soften, about 2 minutes. Add snap peas, garlic, and 1/4 cup water; sprinkle with salt. Sauté until vegetables are just tender and water evaporates, 2 to 3 minutes. Stir in 1 rounded tablespoon pistou. Transfer vegetables to platter; tent with foil to keep warm. Reserve skillet (do not clean).
Heat remaining 1 tablespoon oil in reserved skillet over medium-high heat. Sprinkle salmon with salt and pepper. Place salmon, skin side down, in skillet; cook until skin is crisp, about 3 minutes. Turn salmon and cook until almost opaque in center, about 3 minutes longer. Arrange salmon fillets over vegetables on platter. Spoon some pistou down center of each fillet and serve, passing remaining pistou alongside.