Preheat the oven to 350 degrees.
In a large skillet, heat 1 tablespoon of the olive oil. Brown the lamb over high heat, breaking it into small pieces with your spatula, until nicely browned, about 7 minutes. Season the meat lightly with salt and transfer to a bowl.
Add the fennel and shallot to the pan, along with a tablespoon of olive oil if it seems dry (the lamb, depending on how lean it is, should leave behind enough fat to grease the pan). Sauté the vegetables over medium-high heat until soft and just beginning to brown, 5 minutes. Stir in the chard and season generously with salt. Continue cooking until the greens are very wilted, another 3 minutes. Set aside.
Spread 1/2 cup of the marinara sauce in the bottom of a 9 x 13 casserole dish. Arrange your first layer of noodles on top, making sure they overlap slightly. Slather the noodles with 1/4 cup Greek yogurt. Top with half the lamb and chard mixture, followed by 1/2 cup sauce. Repeat the layers.
Finish the lasagna with a final layer of noodles, Greek yogurt, and marinara sauce, swirling it with your spoon so they mix slightly.
Bake in the oven for 30 minutes, or until the noodles are tender and the top of the lasagna is beginning to brown.
Allow the lasagna to rest for 5 minutes before cutting it into slabs and serving.