Heat oil in large pot over medium heat. Add onion and sauté for about 3 minutes.
Add garlic and sauté for another 2 minutes.
Stir in remaining ingredients. Reduce heat to low and simmer for 20 to 30 minutes.
Preheat oven or toaster oven to 400°F. (I like the toaster oven for these simple snacks.)
Cut zucchinis in half length-wise if using this as your base.
If using Gluten-free bread or pizza dough - roll out dough and lightly toast the bread first to prevent it from getting too soggy.
Spread a thin layer of sauce on base of your choice (zucchini, gluten-free bread or pizza crust).
Add dairy-free cheese if desired and other toppings of your choice.
Place pizza snacks on parchment-lined cookie sheet and bake for about 15 to 20 minutes (bread may take less time). Zucchini takes longer than the bread, so make sure the zucchini is soft.
If serving to children, allow the sauce to cool a bit before serving.