Preheat the oven to 180C/350F/Gas 4.
For the salmon, heat the oil in an ovenproof frying pan until smoking and add the salmon, skin-side down. Fry for 2-3 minutes, or until the skin is crisp and golden. Turn the salmon over and fry for another 1-2 minutes, or until lightly golden. Transfer to the oven to cook for 6-7 minutes, or until the salmon is cooked through.
For the spinach, melt the butter in a clean frying pan and cook the spinach for 3-4 minutes, or until wilted, then season with salt and freshly ground black pepper.
For the roasted tomatoes, heat the oil in an ovenproof frying pan. Add the tomatoes and stir to coat with the oil. Season with salt and freshly ground black pepper, then place into the oven to roast for 5-6 minutes, or until softened.
For the pesto, place all of the pesto ingredients into a food processor and blend to a smooth paste.
To serve, pile the wilted spinach onto a serving plate and top with the seared salmon. Spoon the roasted cherry tomatoes alongside, then drizzle over the pesto dressing. Serve.