Put the olive oil in a large saute pan and place on a high heat. Add the crushed cumin and coriander and cook for one minute, stirring often then add the garlic. Cook for another minute until the garlic starts to colour .
Add the chilli and tomatoes and cook for another two minutes, stirring from time to time, until the tomatoes start to soften.
Add the potatoes, sugar, 1 tsp salt and a good grind of black pepper. Give everything a good stir together.
Transfer to a large parchment lined baking tray. Roast for about 40 minutes, tossing half way through until the potatoes are crispy and cooked through and the tomatoes are breaking down.
Remove from the oven and set aside to cool for 5 minutes before adding the lemon zest and juice and the fresh herbs. Toss gently and serve at once.