Place an oven rack in the center of oven, then preheat to 425°F. Wash and dry the fresh produce. Thinly slice the mushrooms. Halve, peel, and thinly slice the onion. Grate the cheese on the large side of a box grater. Halve the radishes lengthwise, then thinly slice crosswise. Transfer to a large bowl; add the vinegar and season with salt and pepper. Set aside to marinate, stirring occasionally, at least 10 minutes.

In a large pan (nonstick, if you have one), heat a drizzle of olive oil on medium-high until hot. Add the sliced mushrooms in an even layer. Cook, without stirring, 3 to 4 minutes, or until browned. Add the sliced onion and season with salt and pepper. Cook, stirring occasionally, 3 to 4 minutes, or until softened. Turn off the heat.

Crack the eggs into a large bowl; beat until smooth. Add the grated cheese, crème fraîche, and as much of the truffle zest as you'd like. Whisk until thoroughly combined and smooth. Add the cooked mushrooms and onion. Season with salt and pepper; stir until combined.

Place the pie crusts on a sheet pan, leaving them in their tins. Evenly divide the filling between the crusts; season with salt and pepper. Bake, rotating the sheet pan halfway through, 18 to 20 minutes, or until the crusts are browned and the filling is set and cooked through. Remove from the oven. Let stand at least 2 minutes before serving.

While the quiches cool, to the bowl of marinated radishes, add the arugula and 2 teaspoons of olive oil. Season with salt and pepper; toss to combine. Serve the baked quiches with the salad. Garnish the salad with the almonds. Enjoy!