Sunday roast fish

Name: Sunday roast fish
Prep time: 20 min
Cook time: 40 min
Total time: 1 h
Cuisine: European, British
Ingredients: 1 bunch baby (Dutch) carrots, peeled; 4 small parsnips, peeled, halved; 8 garlic cloves (unpeeled); 4 rosemary sprigs, plus extra chopped rosemary (or parsley) to serve; 2 tablespoons olive oil; 100g small shiitake mushrooms, trimmed; 4 x 200g blue eye fillets (or other firm white fish); 16 baby brussels sprouts (or 8 small), halved, blanched for 2 minutes; 2 tablespoons balsamic vinegar (optional)