Spicy bean tostadas with pickled onions & radish salad

2 red onions, 1 thinly sliced, 1 finely chopped

2 limes juice of 1 and 1 cut into wedges

1½ tbsp sunflower oil

2 garlic cloves, finely chopped

2 tsp ground cumin

1 tbsp tomato purée

1 tbsp chipotle paste

400g can kidney bean, drained and rinsed

4 corn tortillas

140g radish, thinly sliced

large handful coriander, roughly chopped