Preheat the oven to 400°. Prick the piecrust all over with a fork. Bake until golden, about 10 minutes. Reduce the oven temperature to 350°.
In a large skillet with a lid, heat 2 tbsp. oil over medium-low. Add the leek; cover and cook, stirring occasionally, until softened, 6 to 8 minutes. Stir in the chard stemsand garlic. Season and cook, stirring occasionally, until tender, about 8 minutes. Stir in 2 cups of the chard leaves. Cook, stirring often, until wilted and almost dry, about 4 minutes; season.
In a large bowl, whisk the creamand eggs. Stir in the cheese and the cooked chard mixture; season with 3/4 tsp. salt and 1/2 tsp. pepper. Transfer to the baked piecrust. Bake until the filling is golden andset in the center, 30 to 40 minutes.
In another large bowl, whisk the remaining 3 tbsp. olive oil with the orange zest and juice. Toss in the chopped radishes and sliced radish greens, carrot, and the remaining thinly sliced chard leaves; season. Serve with the quiche.
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