Southwest Marinade: In a bowl, add all ingredients. Mix well to combine.
Place chicken breasts in marinade. Turn to coat both sides of chicken well. Marinate 4 hours. Place marinated chicken breasts on preheated grill. Cook 4 minutes, turn and cook an additional 4 minutes or until thoroughly cooked.
Chipotle Mayonnaise: In a mixing bowl, combine all ingredients. Mix until well blended.
Smashed Avocado: In a small bowl, combine avocado, lemon juice, salt and cumin. Using a fork, mash avocado and mix well.
Sandwich Build: Split baguette lengthwise. Spread 1 tablespoon of Chipotle Mayonnaise on heel of baguette. Place grilled chicken breast on top of Chipotle Mayonnaise. Place 4 slices red onion rings on top of chicken. Top with 4 slices jalapeño peppers, 2 slices tomato and cilantro leaves. Spread 2 tablespoons of Smashed Avocado on crown of baguette. Close sandwich with crown of baguette.