Place the butter, chipotle pepper, lime zest and lime juice in a small bowl and mix until thoroughly combined. Cover and set aside until the chicken is ready. Preheat an indoor or outdoor grill to medium-high. Brush the chicken with the olive oil and then sprinkle and rub with the cumin, salt and pepper. Grill the chicken for 3 to 4 minutes per side, or until cooked through. Divide the chicken among plates, top each breast with a spoonful of the butter and serve.
Note: Chipotle peppers, which are smoked jalapeño peppers, are sold in cans in the Mexican food aisle. Store the unused peppers in a tightly sealed jar in the fridge. They will keep for several weeks.