Rosemary balsamic lamb with vegetable mash

Name: Rosemary balsamic lamb with vegetable mash
Prep time: 15 min
Cook time: 35 min
Total time: 50 min
Cuisine: European, British, Mediterranean
Ingredients: 320g celeriac peeled and diced; 320g swede peeled and diced; 320g potato peeled and diced; 1 tbsp rapeseed oil; 3 red onions thinly sliced; 550g lean, trimmed lamb steak diced; 1 tsp finely chopped rosemary; 1 tbsp vegetable bouillon powder; 2 tbsp balsamic vinegar; 1 tbsp chopped parsley; 320g spinach to serve; 320g frozen peas to serve