In a large skillet, heat oil over medium-high heat. Once oil is hot, add onion and bell pepper slices. Sprinkle spices over the top and generously salt and pepper.
Cook, stirring occasionally, for 4 to 8 minutes, until edges are browned and vegetables are tender-crisp.
For softer vegetables, once the veggies have browned a bit, turn heat down to medium to keep them from burning, and continue to cook until they reach your desired level of doneness.
For veggies with no bite, add about 1/4 cup of water to the pan once they’ve started to brown. Cook the veggies, stirring often, until water has evaporated and veggies are soft, adding more water by the tablespoon if necessary.