Cheesy bean and lentil bake

Name: Cheesy bean and lentil bake
Ingredients: 2 tbsp olive oil; 1 large onion, finely chopped; 2 sticks celery, finely chopped; 1 large carrot, finely chopped; 1 courgette, finely chopped; 2 garlic cloves, crushed; ½ tsp crushed dried chilli flakes; ½ tsp dried oregano; 100g/3½oz brown basmati rice; 500ml/18fl oz vegetable stock; 2 x 400g tin chopped tomatoes; 400g tin mixed beans in water, drained; 400g tin lentils in water, drained; 2 tbsp tomato purée (sun-dried is nice); 150g/5oz mature cheddar, grated; 2 tbsp breadcrumbs; salt and freshly ground black pepper