Preheat the oven to 180C/350F/Gas 4. Bring a pan of salted water to the boil.
For the griddled fennel, place the fennel slices into a steamer or metal colander, suspend it over the boiling water, and cover with a lid. Steam for 6-8 minutes, or until the fennel is just tender.
Heat a chargrill pan over a medium heat, add the steamed fennel, and cook for 3-4 minutes on each side, or until golden-brown.
For the hot tomato and balsamic dressing, place the tomatoes into a small, non-reactive, ovenproof frying pan over a medium heat. Add the balsamic vinegar, olive oil and garlic, and heat through until the mixture starts to sizzle. Transfer to the oven and cook for 6-8 minutes.
To serve, place the griddled fennel onto a plate and spoon the hot tomato and balsamic dressing over the top.