Fill a large pot with lightly salted water and bring to a rolling boil over high heat. Once the water is boiling stir in the lasagne pasta and return to a boil. Cook the pasta, stirring occasionally until the pasta has cooked through but is still firm to the bite, about 10 minutes. Drain well and return pasta to the pot.
Preheat an oven to 180 degrees C. Grease a 20x30cm baking dish.
Combine the olive oil, onion and garlic in a large frypan. Cook and stir over medium heat until soft, about 3 minutes. Add the sliced chicken; cook, stirring until chicken is lightly browned and no longer pink in the center, about 5 minutes.
Mix in the spinach, black olives and lemon juice. Cook until heated through, an additional 1 to 2 minutes. Stir the chicken mixture into the pasta, add the feta cheese and mix well. Spoon into the prepared baking dish and cover with aluminium foil.
Bake in preheated oven until the pasta is hot and the cheese is melted, about 30 minutes.