Martha and Chef Bryan Sikora make mushroom and autumnal vegetable flatbread sandwiches.
Preheat oven to 400 degrees.
Place beets in a medium roasting pan and add 1/4 cup water; season with 1 tablespoon salt. Cover beets with a piece of parchment paper-lined aluminum foil and transfer to oven. Roast until tender and easily pieced with a paring knife, about 25 minutes. Using a paper towel, peel skin. Thinly slice beets and set aside.
Meanwhile, in a large skillet, heat butter and curry powder over medium heat. Add leeks and cook, stirring, until tender, 6 to 7 minutes. Add peppers and cook, stirring, until tender, about 10 minutes. Add mushrooms and cook, stirring, until steaming and heated through, 5 to 6 minutes. Remove from heat and set aside.
In a medium bowl, add brussels sprouts, ricotta salata, lemon juice, and olive oil; season with salt and pepper and toss to combine. In a small bowl, whisk together yogurt with a splash of water until smooth; season with salt and pepper.
Lay one piece of flatbread on work surface. Place 3 slices of beets over three-quarters of the flatbread; top with 1/4 cup sauteed vegetables, 2 tablespoons brussels sprouts, and 1 tablespoon yogurt. Starting with the covered portion, roll flatbread toward the uncovered portion and place seam side-up; insert a skewer through seam to secure. Repeat process with remaining pieces of flatbread and vegetable mixture. Remove skewers and slice each in half before serving.