Put the berries in a bowl with the sugar, lime zest and orange blossom water, if using, and leave to macerate for an hour while you get on with everything else.
Heat the oven to 170C (150C fan)/325F/gas 3. Mix the first six ingredients for the crumble in a medium bowl. Pour over the melted butter, golden syrup and cream, and stir to combine. Transfer to a medium oven tray lined with greaseproof paper, then bake for 18 minutes, until golden. Leave to cool, then roughly break into a fine crumble with the back of a spoon.
Meanwhile, make the filling. Put the cream, yoghurt, icing sugar and vanilla paste in the bowl of a stand mixer fitted with the whisk attachment and whisk for three to four minutes, until the cream mix has medium peaks that hold their shape (alternatively, whip it by hand). Fold in a teaspoon of the lime zest, then refrigerate until ready to serve.
To assemble the dish, spoon 30g of the cream mix into six small 9cm high x 6cm wide glasses. Top each one with 30g macerated berries and 10g oat crumble, then repeat the layering twice more, so you have three layers of each component, finishing with the crumble on top. Sprinkle over the remaining teaspoon of lime zest and serve at once.