1.Heat 2 teaspoons of the oil in a medium frying pan. Cook bacon, until crisp. Drain on absorbent paper.
2.Combine eggs, water, salt and pepper in a large bowl; beat lightly.
3.Heat a quarter of the butter and 1 teaspoon of oil in same pan on medium heat. When butter is just bubbling, add a quarter of egg mixture to pan; sprinkle on a quarter of onion, mint and feta. Cook, tilting pan, until egg is just set. Slide omelette from pan, fold in half. Repeat with remaining butter, oil egg and filling.
4.Serve omelettes immediately with spinach and bacon.