1. Make vinaigrette by combining shallots, lemon juice and vinegar in a small bowl. Set aside for 5 to 10 minutes to marinate the shallots. Add olive oil in a slow, steady stream, whisking constantly to emulsify. Whisk in salt and pepper, then whisk in mustard. Taste and adjust seasoning with salt if necessary. You should have about 3/4 cup. Use immediately, or transfer to an air-tight container and refrigerate for up to 3 days.
2. For salad, preheat oven to 325 degrees. Spread almonds on a rimmed baking sheet, place in oven and toast, shaking the pan occasionally until nuts take on color and are fragrant, 15 to 20 minutes. Remove from oven, drizzle with olive oil, sprinkle with salt and toss to coat. Let almonds cool slightly, then coarsely chop and set aside.
3. Place turkey in a large bowl. Add a few tablespoons of vinaigrette and toss to coat. Allow turkey to marinate for a few minutes.
4. Add radicchio, frisee and arugula to the bowl with turkey. Drizzle 1/2 cup vinaigrette over salad and toss gently with your hands to coat the leaves evenly. Sprinkle with salt and toss again. Taste for seasoning and add more vinaigrette, a squeeze of lemon juice or salt if needed. Reserve any vinaigrette for another use.
5. Pile salad on a large platter or divide among individual plates. Crumble feta cheese over the top and serve right away.
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