Heat a couple of slugs of extra virgin olive oil in an ovenproof pan, then soften the garlic and courgettes without colouring them, about 10 min.
Remove roughly a third of the courgettes and blend with a ladleful of hot stock and a handful of basil to create a loose green puree.
Stir the orzo into the remaining courgettes, coating it in the oil, season well and pour in the rest of the stock. Bring to a simmer, transfer to an oven at 180C fan/gas 4 and bake until cooked through, rich and thickened, about 25 min.
Stir through the green puree, finish with a dollop of crème fraîche, lemon zest and more basil, then drizzle with olive oil.