Heat 1 tablespoon of the olive oil in a large, deep skillet over medium-high heat. Add the shrimp, season with salt and pepper, and sauté just until they start to turn pink, 2 minutes. Remove the shrimp with a slotted spoon to a plate and set aside.
Return the skillet to medium-high heat and add the remaining 1 tablespoon olive oil. Add the onion and bell pepper and sauté until they start to soften, 2 minutes. Add the garlic and sauté until you can smell it, 1 minute more. Add the tomato sauce, tomato paste, oregano, chili powder, and red pepper flakes, if using. Cook, stirring occasionally, to blend the flavors, 5 minutes. Season with salt and pepper. Stir in the olives if using, the parsley, and the reserved shrimp and cook until the shrimp are cooked through, another 2 minutes.
Serve the shrimp mixture with the tortillas and pass the sour cream and avocado on the side.
Notes
If you’re not thinking about tacos, this is also quite lusty, served over a pile of hot rice or quinoa or tossed with freshly cooked hot pasta.There are several ways to warm your tortillas. Don't forget; it makes a big difference.