Mable's Veggie Loaf was the first vegan dog food recipe I ever used, and it's a good one to start with. The ingredients can all be found at your local health food store. I use pinto beans, lentils, or chickpeas generally, and usually green beans, peas, carrots, and a little bit of broccoli for the vegetables. I always use brown rice, as it is considered more nutritious than white rice. Please note, I have never used the optional ketchup, since I have not been able to find a ketchup that doesn't contain onion powder- a big no-no for dogs (and cats). I don't have loaf pans, so I use my glass baking pans, and it comes out just fine.
Here's what my loaves of Veggie Loaf generally look like when done:
And here we have a slice of Veggie Loaf, a Sam's Yam, and a couple of Mr. Pugsly's peanut butter biscuits.