Boil the corn for 2 minutes, drain well and cool to room temperature. Cut the kernels off the cob and combine them with the next 8 ingredients in a salad bowl.
Preheat your grill to medium-high. Brush the salmon lightly with olive oil; season with salt and pepper. Lightly oil the bars of the grill. Grill the salmon 3 to 4 minutes on each side, or until just cooked through.
Transfer the salmon to a plate. Add the spinach and onion to the salad bowl and toss to combine. Divide the salad among 4 dinner plates. Set a piece of salmon on each salad and serve.