Cook the potatoes until tender then drain.
Heat oven to 190C. Quarter the fennel lengthwise, through the root, then trim off the hard core. Put the fennel into a roasting tin, drizzle with half of the olive oil, then season with salt and pepper. Toss and bake for about 20 minutes, until tender.
Add the tomatoes, olives, garlic potatoes and herbs. Drizzle with the remaining oil and toss well. Return the tin to the oven for 10-15 mins until the fennel is golden and the tomatoes have softened.
Serve warm or at room temperature.