Grill bacon in the oven until crispy, then remove and rest on paper towels. Cut when cold.
Mix olive oil through the mushrooms, then spread over a baking tray. Scatter the salt over the mushrooms and put into a 200°C oven for 30-35 minutes.
When mushrooms are nearly ready, heat the butter and extra olive oil together in a frying pan, until butter is foaming. Add the kidneys and fry over a high heat, turning after 45 seconds.
Cook for a further 30 seconds, then lift out the kidneys, onto a warm plate.
Divide the spinach leaves between plates. Spoon mushrooms onto the spinach leaves, followed by the crumbled bacon, baby beetroot and lastly the cooked kidney halves.
4 tablespoons olive oil
1/2 teaspoon salt
2 teaspoons dijon mustard
1 teaspoon coconut sugar
3 teaspoons red wine vinegar
Mix the dressing ingredients together thoroughly in a small jug.
Drizzle the well mixed dressing over each plateful of salad, and serve.