Chop the sausage and onion roughly then, in a small food processor, blend to a coarse paste.
Place the mince into a large bowl, season to taste with salt and pepper. Add the chorizo paste and, using your hand, mix well.
Form 4 balls, press these down slightly between your palms. Rest the patties until ready to cook.
Heat your BBQ or a griddle pan. Brush the burgers with a little oil, then cook them for 3-5 minutes on both sides, depending on how well cooked through you like it.
Cut in half the buns, grill or toast them cut side down. On the bottom half add some mayonnaise, lettuce or rocket salad and a slice of grilled red pepper. Place the chorizo burger on it and cover with the top half of the bun. Enjoy!