Begin by heating the extra-virgin olive oil in a large skillet over medium heat. Once the oil is shimmering, add the finely chopped onion. Sauté for about 5 minutes, or until the onions are translucent and fragrant.
Next, add the thinly sliced red bell peppers to the skillet. Cook for about 10-12 minutes, stirring occasionally, until the peppers have softened and started to caramelize.
Once the peppers are tender, add the peeled, seeded, and finely chopped tomatoes. Stir well and allow the mixture to simmer for another 5-7 minutes.
Add the chopped chipotle chile in adobo sauce. Stir it into the mixture and let it cook for an additional 3-4 minutes.
Remove the skillet from heat and stir in the coarsely chopped basil. Season the sauce with salt and freshly ground black pepper to taste.
If you prefer a smoother sauce, you can use a blender or food processor at this stage. Blend until you reach your desired consistency.