Preheat the grill to its highest setting. In a food processor or using a stick blender and bowl, blitz together the parsley, oil, capers, garlic and lemon juice until very smooth. This should take roughly 2 minutes. Chop the cherry tomatoes into small pieces - I like to do quarters or eighths, but this is entirely dependent on your patience!
Mix the parsley sauce with the tomatoes to create a vibrant green salsa. Season to taste and set aside. Pat the mackerel fillets dry with kitchen paper to help the fish crisp up under the grill. Place on a roasting tray, skin-side up, with a small piece of baking paper underneath (this helps prevent the fish from sticking to the tray, however you don’t need too much as any excess may burn underneath the grill).
Drizzle the skin with a little olive oil and season generously with some salt and pepper. Grill for 4-6 minutes depending on the size of your fish. The skin should blister and blacken a little and the flesh should be just cooked and flaking nicely.
Serve immediately with the salsa and some fennel fronds and flowers (or any other herbs you have to hand). This recipe is also delicious served with a dry white wine, but then again so is everything…