Cauliflower burrito bowls

Name: Cauliflower burrito bowls
Ingredients: ½ cauliflower, broken into florets; 1 tbsp chipotle paste; 1 tsp ground coriander; ½ tbsp rapeseed oil; 125g brown basmati rice; ½ x 400g can black beans, drained; 2 large tomatoes, deseeded and finely chopped; ½ red onion, finely chopped; 1 lime, juiced; ½ bunch of coriander, roughly chopped; 1 medium avocado, peeled, stoned and sliced; pinch of chilli flakes, to serve (optional)