Preheat the oven to 400°F.
Heat a couple tablespoons of olive oil in a large nonstick skillet over medium-high heat. Working in batches, pan-fry the eggplant slices until golden and tender, about 3–4 minutes per side. Add more oil as needed between batches. Transfer the cooked eggplant to a paper towel–lined plate.
In the same skillet, add more oil if needed and sauté the diced onion and bell pepper for 5–7 minutes until softened. Stir in the garlic and cook for 1 minute. Add the crushed tomatoes, Italian seasoning, salt and pepper. Simmer for 5 minutes, then remove from heat.
In a 9x13-inch baking dish, spread a thin layer of the tomato sauce. Layer in half the eggplant, spoon over half of the sauce, and sprinkle with half the mozzarella. Repeat with remaining eggplant, sauce, and mozzarella.
Sprinkle the Parmesan and panko evenly over the top.
Bake uncovered for 25–30 minutes, or until bubbling and golden on top. Let rest for 10 minutes before serving. Garnish with parsley, if desired.