Whiz cooked beans with blender, adding just enough of the reserved cooking liquid to get a smooth, fairly thick puree.
Heat fat in a heavy bottomed pan, when foaming add the onion, season well and sweat the onion until soft. Add the garlic, chilli (spice or herbs if you like) cook for a further few mins.
Add the pureed beans to the onion mixture and cook for another 10 minutes, turning down the heat after a few minutes to very low and stirring constantly.
Add a little more of the cooking liquid so that you get a nice smooth puree that falls easily from a wooden spoon. Taste and season again. At this stage, you can cool the beans and reheat them when you are ready to eat (cover them with a circle of greaseproof paper or old butter papers to stop the beans forming a skin).
Slice the tomatoes and dress them in salt and pepper, the chilli and a drizzle of olive oil.
Slice the chorizo up into bite-size pieces that can easily be grilled, unless you are cooking them outside on the barbecue, in which case grill the sausages first and then slice them so you don't lose precious pieces in the fire.
Heat a griddle or frying pan until smoking hot, add the chorizo and cook for a few minutes a side until it is looking good and crispy.
Remove to a plate and cut the buns in half. Brush both sides of the buns with the chorizo fat and a little extra oil if you think they need it.
Toast on the grill pan on both sides.
Smear one half of the buns with refried beans and top with the avocado, red onion, chorizo and lettuce. Smear the other half in the mayonnaise, and press down firmly. Eat at once, preferably doused with healthy amounts of the blow-your-head-off habanero salsa or the Fiery roast tomato salsa.