This spicy, chunky salsa is one of the most commonly used in Mexican and Southwestern cooking. It’s a necessary accompaniment to fajitas, but it’s also delicious with any grilled food or as a flavoring for meat loaves, mixed salads, omelets, and even tuna salad. If you can’t find serrano chiles, jalapeños make a milder substitute. The recipe can be easily doubled and will keep, covered, in the refrigerator for 2 days.