Hardboiled eggs: Fill a small saucepan with water up to three quarters. Add a good pinch of salt. This will prevent the eggs from cracking. Bring to a boil. Using a spoon or hand, dip each egg in and out of the boiling water - be careful not to get burnt. This will prevent the egg from cracking as the temperature change won't be so dramatic. To get the eggs hard-boiled, you need around 10 minutes. This timing works for large eggs. When done, remove from the heat and place in a bowl filled with cold water.
Green beans: Fill a small saucepan with water and season with salt. Add the green beans and bring to a boil. Cook until crisp-tender for 4-5 minutes. When done, take off the heat and pour the hot water away to prevent the beans from further cooking.
Mackerel: Make small diagonal slashes on the skin side of the mackerel - don't cut too deep. Season with salt and pepper from both sides.
Heat a pan greased with 1 tbsp oil. Once the pan is hot, add the mackerel fillets, skin side down, and cook over a medium-high heat until the skin is crispy and the meat opaque and cooked. When done, take off the heat and set aside to cool.
When the eggs are chilled, peel off the shells.
Vinaigrette: Whisk the extra virgin olive oil, mustard, and lemon juice together.
Wash and drain the greens in a salad spinner or just by pat drying using a paper towel.
To assemble: Place the greens in a serving bowl and top with the cooked green beans. Add quartered hardboiled eggs and mackerel fillet, and drizzle with the dressing. Enjoy!