In a cast-iron or heavy-bottomed pan, heat the oil over medium-high heat. Add the onions and cook until soft, about 5 minutes. Add the chorizo and garlic, breaking up the chorizo with a wooden spoon to resemble ground meat. Cook through. Add the refried beans with a little water, if necessary, to get a smooth, not-too-dry consistency, and stir to combine with the chorizo and onions.
Make the tacos. Arrange the tortillas on a plate using two for each taco. Add the chorizo mixture, cheese, a few radish slices, a few cilantro leaves and a shake of hot sauce. Repeat for the remaining tortillas and filling.