Line a 1-inch-deep, 8-inch square baking tray with greaseproof paper, leaving excess paper hanging over the sides.
Pour the vegetable stock into a medium saucepan and bring to a boil. Whisk in the polenta and keep whisking for around 2 minutes, until the mixture starts to thicken. Once thickened, remove the pan from the heat, add the seasoning, herbs, and lemon zest and stir well.
Pour the mixture into the lined baking tray and smooth flat with a spatula, then let chill in the fridge to set for around 2 hours.
Preheat the oven to 350° F and remove the polenta from the fridge. Lift the firm block of polenta out of the tray using the overhanging paper as handles. Cut the polenta into chunky chips, brush with the olive oil, scatter on a baking tray, then bake in the oven for 20 to 25 minutes, or until golden. Season with salt and pepper, then serve straight away.