I like having refried beans for the first layer. It helps all of the other toppings hang on.
If you have a pressure cooker, then you can have refried beans in no time at all. I put the dry beans in the cooker, add water and a little oil, and bring to high pressure. Cook at high pressure for 10 minutes and then turn off heat and allow pressure to drop on its own. Once I can open the cooker, I fill the food processor with beans, a little olive oil, and a clove of garlic. Process until smooth (adding water to thin as needed), add salt to taste, and there you go! The whole process takes about 1/2 hour.