Add the calamari rings to the skillet and cook for 2-3 minutes until they turn opaque. Be careful not to overcook them, as they can become tough.
Stir in the diced tomatoes (with juice), Kalamata olives, capers, and oregano. Season with salt and pepper. Let the mixture simmer for about 5 minutes, allowing the flavors to meld.
Add the cooked pasta to the skillet, tossing to combine. If the sauce is too thick, add reserved pasta water a little at a time until you reach your desired consistency.
Remove from heat and stir in the fresh parsley and lemon juice. Serve immediately.
Notes
For a milder dish, reduce or omit the red pepper flakes.
Add a handful of spinach or arugula to the pasta for extra greens and nutrition.