In a medium bowl, combine the onion, tomato, avocado, cilantro, Worcestershire sauce, lime juice, salt and pepper. Mix well and set aside.
Place the bread slices on a flat work surface. Spread 1 tablespoon of butter evenly over one side of each slice of bread.
Warm a skillet over medium heat for 3 to 5 minutes. Layer each sandwich as follows: Slice of bread, butter side down, ½ cup shredded pepper jack cheese (or 2 slices), ½ of the avocado mixture, ½ of the crushed tortilla strips, ½ cup shredded pepper jack cheese (or 2 slices) and slice of bread, butter side up.
Place sandwiches onto the hot skillet. Cook on each side for about 3 to 4 minutes, or until the bottom layer of cheese begins to melt around the edges. Cut in half and serve!