In a medium-sized skillet, heat over medium heat and add slices of bacon, allowing them to cook until crispy, about 8–10 minutes. Once done, drain on paper towels to absorb excess grease, reserving 2 tablespoons of bacon oil in the pan for the next steps.

With the reserved bacon oil still in the skillet, add thinly sliced onions and sauté over medium heat until they turn golden brown, approximately 10–15 minutes.

While the onions are caramelizing, combine mayonnaise and adobo sauce in a mixing bowl. Stir well until creamy and evenly mixed.

Using the same skillet, add slices of your chosen sandwich bread and toast them for about 1–2 minutes per side until golden brown.

On one slice of the toasted bread, spread the chipotle mayo. Layer the caramelized onions, followed by crispy bacon, fresh tomato slices, and arugula.

Place the second slice of toasted bread on top, pressing down gently to secure all the layers. Slice in half if desired, and serve immediately.