Preheat grill to medium setting and place the chicken breast under the grill. Whilst the chicken is grilling, slice open the baguette down the middle. Spread butter over one side, and the pesto over the other.
Turn over the chicken breast and add the bacon rasher to the grill. Whilst they finish cooking, slice the tomatoes in half and place in the baguette along with the spinach leaves.
When the chicken is cooked and the bacon crispy, remove both ingredients from the grill onto a chopping board or plate. Slice the chicken and then place inside the baguette along with the bacon.