Preheat your oven to 350°F (175°C).
In a skillet, brown the ground beef with chopped onion and minced garlic. Once it's cooked, drain any excess fat.
Add the ground beef back to the skillet, and pour in the jar of spaghetti sauce. Simmer the mixture on low/medium heat, covering it, for about 10 minutes.
In a small bowl, mix together the ricotta cheese, egg, and parmesan cheese.
Grease a 9x13 casserole dish to prevent sticking.
Chop the zucchini into even-sized pieces. Before sautéing the zucchini, sprinkle a bit of salt on it and let it sit for around 10 minutes. This helps to remove excess water and prevent a watery lasagna.
Melt butter and sauté the zucchini in a small skillet for 3-5 minutes. You don't want it to become too soft. Remove it from the skillet and place it on paper towels to drain moisture.
Now it's time to layer the lasagna! Start by covering the bottom of the casserole dish with half of the spaghetti sauce.
Next, layer the sautéed zucchini on top of the sauce.
Spoon the ricotta cheese mixture in dollops over the zucchini and use the back of a spoon to spread it out evenly.
Add half of the mozzarella cheese as the next layer.
Repeat the layers with the remaining spaghetti sauce, zucchini, ricotta cheese, and mozzarella cheese.
Sprinkle 1 tablespoon of Italian seasoning on top for extra flavor.
Cover the casserole dish with aluminum foil and bake it in the oven for 20 minutes. Then, remove the foil and bake for an additional 20 minutes.
Allow the lasagna to rest for approx 15 min before serving. Enjoy!