Mix together tomato, cilantro, onion, garlic, jalapeno, lime juice, and a pinch of salt and pepper in a small bowl.
Bring a large pan to boil with about 2 inches of water and vinegar. Add a pinch of salt to the water. Crack egg into a small custard bowl and gently add to the boiling water. Immediately cover and turn off the heat. Let your egg cook for about 6-10 minutes, depending on your desired doneness.
Serve breakfast by layering salsa (or pico de gallo) on top of a fresh, warmed corn tortilla. Add the egg. Sprinkle with cheese.