Preheat oven to 375°F (190°C). Lightly grease a 9x13 inch baking dish. Place zucchini slices on paper towels and sprinkle with salt. Let them sit for 15-20 minutes to draw out excess moisture. Pat dry with paper towels.

In a large skillet, heat olive oil over medium heat. Add onion and cook until softened, about 5 minutes. Add garlic and red bell pepper and cook for another 3 minutes. Stir in crushed tomatoes, tomato sauce, basil, oregano, salt, and pepper. Bring to a simmer and cook for 15 minutes, stirring occasionally.

In a mixing bowl, combine ricotta cheese, Parmesan cheese, parsley, egg, salt, and pepper. Mix well.

Spread a thin layer of tomato sauce mixture in the bottom of the prepared baking dish. Layer with zucchini slices, overlapping slightly. Spread half of the ricotta cheese mixture over the zucchini. Sprinkle with 1/3 of the mozzarella cheese. Repeat layers: tomato sauce, zucchini, remaining ricotta cheese mixture, and another 1/3 of the mozzarella cheese. Top with remaining zucchini slices and the remaining tomato sauce. Sprinkle with the remaining mozzarella cheese.

Cover the baking dish with foil and bake for 30 minutes. Remove the foil and bake for another 15 minutes, or until the cheese is melted and bubbly and the zucchini is tender.

Let the lasagna rest for 10-15 minutes before slicing and serving.