Cut the pumpkin flesh as you would a melon, into long, half-moon-shaped slices roughly 1cm thick. Heat the olive oil in a large shallow pan and fry the pumpkin with the garlic clove for about 3 mins, discarding the garlic as soon as it colours. You may need to do this in 2 batches. When all the pumpkin slices are fried, return them to the pan, draining off any excess oil first. Take off the heat.
Dredge the pumpkin slices with the sugar and cinnamon. Mix well, then sprinkle with the vinegar, mint and pepper to taste. Cover with a lid or plate, and leave to infuse for at least 15 mins before serving warm or cold.