Remove the tomatoes from the vine and wash. Preheat the oven to 200°C/gas mark 6. Toast the bread, then remove the crusts and blitz in a food processor to make crumbs. Add the herbs, oil and garlic and pulse briefly to mix. Season.
Halve the tomatoes and put one layer into a shallow ovenproof dish. Spread the cut surfaces with a little mustard then generously cover with the herb crumb mix. Bake for 15-20 minutes, until the topping is crunchy and lightly browned.