Cod anchovy bake

Name: Cod & anchovy bake
Ingredients: 1 large or 2 medium potatoes, sliced into 5mm-thick rounds (about 280g); 1 onion, thinly sliced (about 160g); 1 tbsp thyme leaves; 10g anchovies, finely chopped; 1 tbsp olive or rapeseed oil; 1 red pepper, quartered, deseeded and sliced; 2 large tomatoes, roughly chopped (about 250g); 1 tsp white wine vinegar; ½ tsp vegetable bouillon powder; 1 garlic clove, finely grated; 2 skinless, boneless cod loins (280g); 25g cheddar, finely grated; 250g baby spinach, wilted, to serve