Heat a stock pot to medium. Add oil and sliced onion and sauté for 10-15 minutes, stirring often.
In a blender, combine garlic, pineapple, chipotle peppers, adobo sauce, lime juice, salt, smoked paprika, cumin and water. Blend until smooth.
Add portobellos to onions. Add sauce and simmer over medium heat for 15-20 minutes, until the liquid reduces.
Serve in a warmed tortilla with avocado or guacamole, cilantro and a squeeze of lime juice.
