(Mix the meat loaf ingredients together, without the egg, a day ahead. Cover with plastic wrap and refrigerate. When ready to cook, mix in the egg, shape, and bake.)
1 1/2 pounds ground turkey
1 small yellow onion, chopped
1/2 cup bread crumbs
1 egg, beaten
1 cup grated Parmesan
2 tablespoons plus 2 teaspoons Dijon mustard
1 cup flat-leaf parsley, chopped
1 7-ounce jar roasted red peppers, cut into 1/2-inch pieces
kosher salt and pepper
1 tablespoon white wine vinegar
3 tablespoons extra-virgin olive oil
6 cups mixed greens
Heat oven to 400° F.
Combine the turkey, onion, bread crumbs, egg, Parmesan, 2 tablespoons of the mustard, the parsley, red peppers, 3/4 teaspoon salt, and 1/2 teaspoon pepper in a large bowl. Shape the meat into an 8-inch loaf and place in a baking dish. (See Tip, below.)
Bake until no trace of pink remains (internal temperature should be 165° F), about 45 minutes. Transfer to a cutting board and let rest 15 minutes before slicing.
Whisk together the remaining mustard, the vinegar, oil, 1/4 teaspoon salt, and 1/4 teaspoon pepper in a small bowl.
Divide the greens among individual plates and drizzle the vinaigrette over the top. Serve with the sliced meat loaf.