1. Preheat oven to 375ºF. In a small bowl, combine mayonnaise, jalapeños, lime juice and salt in a small bowl. Season with pepper. Combine tuna and avocado in a medium bowl. Gently fold mayonnaise mixture into tuna mixture.
2. Arrange English muffins in a single layer on a baking sheet. Top each muffin half with 1/4 of tuna mixture, 1 slice of tomato and 1 slice of cheese. Bake until cheese has melted, about 10 minutes.