Rub the chicken with olive oil, salt and black pepper and heat a large skillet over medium-high heat.
Cook the chicken for 4 to 6 minutes per side, until browned and 165°F inside, then rest it for 5 minutes.
Cook the bacon in a separate skillet over medium heat for 8 to 10 minutes until crisp and drain it on a rack.
Toast all 12 bread slices and spread one side of each with mayonnaise.
Build the lower layer of each club with 1 toast, 1 lettuce leaf, 1 chicken cutlet and 1 tomato slice.
Add a second toast spread-side up, press one-fourth of the mashed avocado over it and top with 2 bacon slices, 1 lettuce leaf and 1 tomato slice.
Close with the third toast, secure each sandwich with 2 picks and cut it diagonally.