How to Make It
Roast the jalapeños over a gas flame until charred all over. Transfer the jalapeños to a bowl, cover and let cool. Peel, stem and seed the jalapeños, then cut them lengthwise into thin strips.
In a large nonstick skillet, arrange the pork belly slices in a single layer. Season with salt and pepper and cook over moderate heat, turning once, until browned and crisp, about 8 minutes. Pour off all but 2 tablespoons of the fat and add the spinach to the pork in the skillet. Season with salt and pepper and stir until the spinach is wilted. Crack the eggs into the skillet and cook for 2 minutes. Using a wide spatula, gently turn the eggs with the pork and spinach, trying not to scramble the eggs. Cook just until the whites are set but the yolks are runny, about 2 minutes. Sprinkle with the lime juice.
Spread the mayonnaise on the toasted rolls and sprinkle with the sesame seeds. Using a spatula, divide the filling between the rolls. Top with the roasted jalapeños, cotija cheese, cilantro leaves and tomato slices. Close the tortas, cut them in half and serve right away.