Spicy bean avocado quesadillas

Name: Spicy bean & avocado quesadillas
Ingredients: 1 small red onion, halved and thinly sliced; 1 lime, ½ juiced, ½ cut into wedges to serve; ½ tbsp rapeseed oil, plus a drop; 1 large garlic clove, finely grated; 2 tsp smoked paprika; 1 tsp ground cumin; 400g can black beans; 1 tomato, chopped; 1 tbsp tomato purée; 1 tsp vegetable bouillon powder; 2 large wholemeal tortillas; 1 avocado, peeled, stoned, halved and sliced; 2 tbsp chopped coriander, plus a few sprigs to serve