Preheat the oven to 160°C/140°C fan.
Pat the pheasant breasts dry with a paper towel. Put the flour and a little salt and pepper into a bowl, add the pheasant breasts and toss to coat.
Heat the olive oil and butter in a frying pan over a medium heat. Add the pheasant breasts to the pan and fry for 3 minutes on each side until brown.
Transfer the pheasant breasts to an oven-proof dish. Add the bacon lardons to the pan and fry until golden. Using a slotted spoon, add the lardons to the pheasant breasts in the dish.
Add the stock and orange juice to the frying pan and simmer until the liquid has reduced by half.
Next add the orange zest, cream and mustard and stir well. Reduce again until the sauce thickens a little.
Add a handful of baby spinach leaves to the sauce and cook until wilted. Season the sauce and carefully stir in the orange segments.
Pour the sauce over the pheasant breasts and lardons, cover and cook in the preheated oven for 20-25 minutes until the pheasant breasts are cooked through.
Serve immediately.