Simmer the carrots in boiling salted water until tender but not soft, about 4 minutes.
Heat a frypan and dry-fry the cumin and coriander seeds for 2 minutes or until aromatic. Transfer to a mortar and pestle or a spice grinder and crush them up.
Add the butter to the frypan. When melted, add the spices, garlic and ginger. Cook 1 minute. Add the carrots and toss to coat with butter. Sprinkle with mint and lemon zest then transfer to a salad dish to cool.