Carrots, red bell peppers, green beans, broccoli, cabbage, etc. are all going to work in this recipe. Avoid vegetables that take really long to cook like potatoes and sweet potatoes. You can add green leafy vegetables (like spinach, kale, etc.) at the end because they take very little time to cook. Frozen vegetables are another great option. They are cheap and you can also save them in your freezer for months. This way you will always have vegetables on hand.