Strips of zucchini stand in for lasagna noodles and ground turkey is swapped in place of ground beef, adding texture and flavor in this healthy, vegetable-filled take on the Italian classic.
Make the sauce: Pulse tomatoes with juice in a food processor until finely chopped. Heat oil in a large straight-sided skillet over medium heat. Cook onion and red-pepper flakes, stirring occasionally, until onion is tender, about 8 minutes. Add turkey; cook, breaking up any large pieces, until browned, 3 to 4 minutes. Add tomatoes; bring to a boil. Reduce heat; simmer until thick, about 20 minutes. Stir in oregano and salt. Let cool.
Make the lasagna: Preheat oven to 375 degrees. Slice zucchini lengthwise into thin strips (about 1/8 inch thick) using a mandoline or a sharp knife. Place 5 or 6 zucchini slices, overlapping slightly, in the bottom of an 8-inch square baking dish. Top with 1 cup sauce. Dot with 1/4 cup ricotta. Repeat twice with zucchini, remaining sauce, and 1/2 cup ricotta, alternating direction of zucchini. Top with remaining zucchini, alternating direction; brush with oil. Dot with remaining 1/4 cup ricotta. Season with pepper. Bake, uncovered, until lasagna bubbles and top browns, 50 to 60 minutes. Let stand for 10 minutes. Garnish with oregano.