Roughly chop the chipotle chile and reserve 1 tablespoon of adobo sauce from the can. Halve and thinly slice the onion. Strip the oregano leaves from the stems. In a small bowl, stir together the paprika and cayenne. Sprinkle the chicken liberally with salt and pepper.

In a large high-sided pan, heat the canola oil over medium-high heat.  Add the chicken in a single layer and sear until golden on the outside, 4 to 5 minutes per side. Remove to a plate.

Add the onions and oregano to the same pan over medium heat and cook until the onion is translucent, about 5 minutes. Add the paprika and cayenne and cook for 1 minute. Add the vinegar and Worcestershire and cook until reduced by half, 1 to 2 minutes.

Add the brown sugar, crushed tomatoes, beer, chopped chipotle, and reserved adobo sauce and stir to combine. Increase the heat to high and bring to a boil, then return the chicken to the pan, nestling it in. Cover, reduce the heat to medium-low, and braise until the chicken easily shreds when pulled with a fork, about 1 hour.

Uncover and carefully shred the chicken with 2 forks. Raise heat to medium and bring to a simmer. Simmer, uncovered, until the sauce is reduced by half, about 10 minutes.

Serve over rice and garnish with guacamole, salsa and sour cream.

Heat the chicken. Toast the buns, cut side down, until golden brown. Spread both sides of each bun with some of the mayonnaise. Place some of the shredded lettuce on the bottom of each bun. Top with the warmed chicken, more of the lettuce and 3 pickles per sandwich.