Begin by preparing all the ingredients.
Remove the skin from the chorizo and slice it into ¼ inch (5 mm) rounds. The onion needs to be peeled, sliced in half and then each half sliced as thinly as possible so you end up with little half-moon shapes. Remove the stalk from the pepper and then halve it, scooping out the seeds. Slice it first into quarters and then each quarter into thin slices. The tomatoes need to be skinned, so pour boiling water over them, leave for 30 seconds, then drain and slip off their skins. Slice each tomato in half, squeeze each half gently to remove the seeds, then chop the flesh into small cubes. Peel and finely chop the garlic. You can watch how to skin tomatoes in our Cookery School Video
Next take a large, heavy-based frying pan, place it over a high heat and add the olive oil. When the oil is really hot, brown the chorizo pieces, tossing and turning them around until they turn slightly brown at the edges. Using a slotted spoon, transfer the chorizo from the pan to a plate. Next add the onion and pepper to the pan and toss these around, keeping the heat high, until they're nicely tinged brown at the edges and softened, which will take 5-10 minutes. Now add the tomatoes and garlic and cook for 1 minute more, then return the chorizo to join the rest of the ingredients. Finally, give everything a good mix and season with salt and freshly milled black pepper.
Then remove the pan from the heat and divide the mixture between the two gratin dishes. Carefully break two eggs side by side on top of the mixture in each dish, season them, then sprinkle them with the grated cheese. Place the dishes on the baking sheet on the top shelf of the oven to cook for 12-15 minutes (or a little longer, depending on how you like your eggs). I think this needs some quite robust red wine and some warm crusty baguette served alongside.