Peel the garlic and cut into thin slices. Wash the rosemary and shake dry. Chop 1 sprig coarsely. Pluck off the rest of the needles and chop them. Peel and wash sweet potatoes and cut them into small pieces.
Wash the fillets if necessary and dab dry. Season with salt, pepper and chopped rosemary. Wrap the bacon tightly around the fillets. Heat 1 tablespoon of oil in a frying pan. Fry the fillets on all sides at high heat for about 5 minutes.
Place the fillets on an oiled baking tray. Spread sweet potatoes all around. Sprinkle garlic and rosemary pieces over them, drizzle 2 tablespoons of oil over the potatoes and season with salt and pepper. Bake in the preheated oven (electric cooker: 150 °C/circulating air: 125 °C/gas: level 1) for 20-30 minutes.
Peel and finely chop the onion. Clean the spinach, wash thoroughly and drain. Heat 1 tablespoon of oil in a saucepan. Sauté the onion until transparent. Add dripping wet spinach, cover and stew for about 5 minutes until it has collapsed.
Season with salt, pepper and lemon juice.
Wrap the fillets in aluminium foil and let them rest for a short time. Then cut into slices. Serve with sweet potatoes and spinach.