Preheat large non-stick skillet on medium heat and add olive oil. Add peppers and onions, sprinkle with salt and pepper.
Stir, cover and cook for 10 minutes, stirring occasionally.
Half way through add garlic and keep cooking.
Turn off heat, add parsley, stir and let peppers sit for 5 minutes to allow flavors to meld. Serve hot or cold.
Notes
To store leftovers: You can keep leftovers in an airtight container in the refrigerator for 4-5 days. Eat cold or you can reheat them in the microwave.
Can I freeze bell peppers? I would not recommend to do so because their texture will change significantly.