Preheat the oven to 190°C. Arrange the sweet potatoes and garlic in a roasting tin. Drizzle the olive oil over the top, toss to coat and season with salt and pepper. Roast the sweet potatoes in the oven for 30 minutes. Add the big brown sliced mushrooms, portabellini mushrooms and broccolini. Return to the oven for 15 minutes, stirring once. Add the baby spinach, orange zest and juice and roast in the oven for 3 minutes, or until the spinach just starts to wilt. Remove from the oven and season with salt and pepper.