Wash the vegetables thoroughly and cut them into bite-sized pieces.
Add cooking oil to a pan and preheat over medium heat.
Add firm vegetables like onions, carrots, and bell peppers first, and stir-fry them.
Add the remaining vegetables such as zucchini and broccoli, and stir-fry.
Season with salt and pepper.
When the vegetables are cooked to your liking, turn off the heat and transfer to a plate.