Heat the oil in a large frying pan, add the onion and cook for 5 minutes until softened. Stir in the garlic and chillies and cook for a further 1 minute. Add the canned tomatoes and sugar and bring to the boil, then season. Reduce the heat and simmer for 10 minutes, topping up with water if necessary.
Add the plum tomatoes and cook for 3 minutes. Using the sliced tomatoes as a base, form 4 indentations in the sauce. Crack an egg into each one, cover with a lid or piece of foil and cook over a medium heat for about 5 minutes, or until the egg whites are cooked through.
Remove the lid and scatter over the crumbled cheese and chopped coriander, then warm through the tortillas in a preheated oven, 220°C (450°F), Gas Mark 8, for 3–5 minutes to soften.
Spoon some tomato and egg mixture into each tortilla and serve.