Heat the vegetable oil in a large skillet over medium heat. Stir in the sausage, and cook until crumbly and just slightly pink, about 5 minutes. Stir in the diced potato and onion. Continue cooking until the potatoes are tender and have lightly browned, 10 to 15 minutes.
Once the potatoes are tender, stir in the mixed vegetables until hot. Season to taste with salt and pepper. Sprinkle with Cheddar cheese before serving.