1. Cut pork into 2 pieces. Place in a slow cooker with onions. Using a blender, combine orange juice, pineapple juice, garlic, chipotles, herbs, salt and pepper. Liquefy, and pour into slow cooker. Cook on low for 4 hours until meat is tender and shreds with a fork. After shredding, cook for 1 more hour on high. Let cool before making sandwiches.
2. Cut each roll in half. Pull out some bread in the top of the rolls to make a trench. Fill each top half with 1/4 cup Cotija cheese. In a bowl, combine the chipotle and mayonnaise. Spread onto the bottom halves of rolls. Top each with meat, cilantro, 2 pineapple slices and sliced avocado. Press a top half of roll onto the top of each sandwich.
3. Heat a grill pan or panini press to high. Spray with cooking spray. Add sandwiches, two at a time. Grill on both sides for about 2 minutes per side, while pressing sandwiches down with a spatula or grill press.

Calories: 827, Fat: 43 g (14 g Saturated Fat), Cholesterol: 127 mg, Sodium: 2107 mg, Carbohydrates: 63 g, Fiber: 5 g, Protein: 43 g.