Place the vinegar, red onion and dates in a bowl. Add a pinch of salt and mix well with your hands. Leave for 20 minutes and then drain the leftover vinegar.
While the dates and red onion are marinating, heat the butter and half of the olive oil in a medium pan. Then add pita bread, almonds and chilli flakes and cook for 6 to 8 minutes or until the pita bread is crunchy and golden brown. Set aside to cool.
Place the spinach in a mixing bowl, then add dates, red onion, remaining olive oil, lemon juice and a pinch of salt. Toss gently, season to taste and serve immediately.