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 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.