Preheat a barbecue or indoor grill to medium high. Heat 1 Tbsp of the oil in a skillet over medium heat. Add the corn, onion and garlic and cook 4 to 5 minutes. Add the tomatoes, stock and thyme and bring to simmer. Reduce the heat to low and reserve the sauce until the salmon is cooked. Brush the salmon with the remaining oil; season with salt and pepper. Grill, lightly oiling the surface first if prone to sticking, 3-4 minutes per side, or until just cooked through. Season the corn/tomato mixture with salt, pepper and lemon juice. Divide and spoon on to 4 dinner plates. Top with salmon, garnish with thyme sprigs and lemon slices and serve.