Preheat the oven to 350°F. To make the "risotto," heat 1 tablespoon of the oil in a small pot over medium heat. Add onions and bacon and cook, stirring occasionally, until bacon is crisp. Stir in orzo and cook for 1 minute more. Add half of the chicken stock and simmer, stirring constantly, until liquid has evaporated. Stir in remaining stock and zucchini and simmer, continuing to stir constantly, until orzo is tender and liquid is almost evaporated. Add Robiola and tomato and stir until cheese is melted. Season with salt and pepper.

Meanwhile, season lamb with salt and pepper. Heat a large oven-proof skillet over medium high heat. Add remaining 1 tablespoon oil and heat until hot but not smoking. Add lamb and cooking, turning occasionally, until deep golden brown on all sides. Set skillet aside. Transfer black trumpet mushroom dust to a large plate and set aside. When lamb is just cool enough to handle, brush all over with Dijon mustard, then roll in mushroom dust to coat. Roast in oven for 5 to 6 minutes, or until done to your liking. Transfer to a cutting board, set aside to let rest for five minutes, then slice.

To serve, spoon orzo onto the center of a serving platter. Arrange lamb around orzo and garnish with herbs and a pinch or two of fleur de sel.