Almost anything except for chocolate, salt, peppers, onion, green onion or milk can be used for dog meals/treats. I make biscuits simplly; combine, flat in square, bake and cut.
Flour, an egg, soy milk or water to shape and dashes of parmesan cheese is very easy.
Or meety flavored biscuits can work too. Use homemade chicken broth (simply boiled) instead of water or soy milk.
Pumpkin or mashed sweet potatoes sounds yummy. I'm sure the dogs love them as well as humans
Interesting thing is there are substitutes, i.e. for sugar, it can be honey; for milk, soy milk.
Although as you know onions are never to be used, a small amount of garlic or ginger is OK to dogs.