Place the chicken breast on a flat surface and cover with parchment paper. Roll the top with a rolling pin so the chicken flattens. This will help the chicken cook faster and evenly.
In a mixing bowl, combine the smoked paprika, chili powder, garlic powder, cayenne pepper, salt, and black pepper. Pat the chicken with a paper towel and rub the seasoning all over it.
Heat a large skillet over medium heat and drizzle with olive oil. Place the chicken in the olive oil and cook on both sides for about 6-8 minutes. The chicken is done when there is no pink in the center. Finish in the oven at 375F for about 10 minutes if necessary.
Preheat the oven to 375F. Line a baking sheet with parchment paper and place the wire rack on top. Line the bacon slices flat next to each other on the rack. Cook in the oven for about 15 minutes. Leave a minute or two longer for crispier bacon.
Meanwhile, make the homemade ranch dressing. In a mixing bowl, combine the sour cream, buttermilk, mayonnaise, garlic, salt and pepper, dill, chives, and lemon juice, and whisk until everything is well incorporated and creamy.
To assemble the sandwiches, spread one of the bread slices with dijon mustard. Layer the chicken, bacon slices, cheese, and lettuce on top. Drizzle with ranch dressing.
Spread some of the dijon mustard on the second bread slice and top the sandwich with it. Slice in half diagonally and serve.