1) Position a rack in the centre of the oven and preheat to 200C/Gas 6. Heat olive oil in a medium skillet over medium-high heat. Squeeze excess water out of spinach. Add spinach and spring onions and cook, stirring, until dry, about 4 mins. Transfer to a colander and press with the back of a spoon to remove the last bit of moisture. Brush 4 (175g) ramekins with some olive oil and put on a baking sheet.
2) Put spinach mixture, eggs, single cream, bread crumbs, mint, salt, black and cayenne peppers, and nutmeg in a food processor and pulse until spinach is finely chopped. Remove blade and stir in feta cheese. Divide mixture evenly among ramekins. Bake until set around the edges but still slightly soft in the centre, about 20 mins. Turn oven off, leaving pies inside to set, about 5 mins more.
3) Run a knife around edge of each pie and invert onto plates; spoon some tomato salad around each and serve.
4) For the Greek tomato salad: Toss tomatoes with pepperoncini and olives in a salad bowl. Add olive oil, lemon juice, oregano, and salt and black pepper to taste. Toss again.