Preheat oven to 425 degrees. Line a large rimmed sheet pan with parchment paper.
Slice zucchini, 1/4 - 1/2 inch slices. If there's excess moisture on the zucchini use paper towels to dab it off. Put it in a bowl and drizzle with 1 tablespoon of oil. Toss until well coated. Place zucchini on the sheet pan in a single layer, it's okay if the edges overlap. Sprinkle salt and pepper over the top. Roast in oven for 20-25 minutes, the edges will be brown. While the zucchini is roasting cook the sausage
In a large skillet over medium heat, cook the sausage with onion and garlic until the meat is browned and onions are translucent. Remove from heat, drain excess grease and return to skillet. Stir the sauce into the sausage.
In a medium bowl, stir together the ricotta, parmesan, egg, parsley, basil and salt until well combined.
Spread all the meat sauce evenly over the zucchini. Drop spoonfuls of cheese mixture evely over the sauce, Use the back of spoon to spread it out a bit. Top with the mozzarella cheese. Bake until the cheese is melted and it's bubbly around the edges, about 10 minutes. Turn the oven to broil. broil for 2-3 minutes to brown the top. Watch closely not to burn. Let sit for 15 minutes before serving.