Heat the olive oil in the skillet over medium-high heat until hot and fragrant. Add the peppers and onions, sprinkle with the oregano, cumin, and salt, and stir. The skillet will be very full at first, but the veggies will cook down over time.
Cook until the veggies are tender and slightly charred, stirring occasionally with a wooden spoon and scraping up any brown bits on the bottom of the skillet. For firmer veggies, cook for ~7 minutes. For softer and more charred veggies, cook for 10 to 15 minutes (or longer). Season with more salt as desired.
Remove from heat and serve in fajitas, tacos, or burritos.
To make this recipe spicier, add sliced jalapenos.
Store leftovers in an airtight container in the fridge for 3 to 5 days. You can eat them cold, or you can reheat them in the microwave on high for 1 to 2 minutes.