Put the chicken breast between two pieces of cling film and bash with a rolling pin or pan to about 1cm thick. Mix the chipotle paste with half the lime juice and spread over the chicken.
Heat a griddle pan over a high heat. Once hot, cook the chicken for 3 mins each side until cooked through, adding the cheese for the final 2 mins of cooking. Add the bun, cut-side down, to the griddle pan to toast lightly. Season the chicken.
Meanwhile, mash the avocado with the remaining lime juice. Stir in the cherry tomatoes, jalapeño and garlic, and season with a little salt. Spread over the base of the bun, then add the chicken followed by the top of the bun.