Heat oven to 190C/170C fan/gas 5. Halve and quarter the fennel through the root, then trim off the hard core. Slice the fennel and tip into a roasting tin with the olive oil, salt and pepper. Toss the fennel in the oil until it is glistening. Roast for 20-25 mins, until starting to soften.
Add tomatoes, olives and potatoes and stir well. Return to the oven for 10-15 mins until the fennel is tender, with a bit of crunch. Tip into a warm dish to serve.