Cut the salmon into 4 pieces at a 45-degree angle. Place on a plate and season with salt and pepper. Drizzle on the lemon juice, soy sauce and sesame oil. Turn over and repeat steps to season both sides of fish.
In a large skillet, heat 2 teaspoons of the olive oil over medium-high heat, add the onion and saute for 5 minutes until soft. Add garlic and cook for 1 minute. Stir in Rainbow Chard and 3 tablespoons of water. Cover and cook for 5 minutes, stirring frequently. Greens should be tender and bright green. Sprinkle with a pinch of salt and stir.
In a separate skillet, heat the remaining 2 teaspoons oil over medium high heat; let skillet get hot but not smoking. Add the salmon pieces in a single layer and sear on one side, cooking for 5 minutes; do not overcook. Pour extra juices from plate onto salmon while cooking, flip salmon and cook for 1 more minute. Divide greens among 4 plates, and place a piece of salmon on top of each pile of greens. For a nice presentation, add a lemon twist.