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adjust oven rack to top position and heat broiler to high. bring a large pot of salted water to a boil. once water is boiling, add penne to pot. cook until al dente, 9-11 minutes. reserve ¾ c pasta cooking water, then drain.
heat a large drizzle of olive oil in a large, preferably ovenproof, pan over medium-high heat. add zucchini and cook, stirring, until just browned, 4-6 minutes. stir in onion, garlic, and season with garlic powder, basil, rosemary, cayenne pepper, oregano, and fennel. cook, stirring, until onion is softened, 3-5 minutes. season with salt and pepper.
add marinara sauce, penne, and reserved pasta cooking water to pan with veggies; stir to combine and season with garlic powder, basil, rosemary, cayenne pepper, oregano, and fennel. simmer until warmed through, 3-4 minutes. stir in half the parmesan. season with plenty of salt and pepper. remove pan from heat. if your pan is not ovenproof, transfer pasta now to a baking dish.
in a small bowl, stir together panko, remaining parmesan, and a drizzle of olive oil. top pasta with mozzarella, then panko mixture.
broil pasta on top rack until panko is golden brown, sauce is bubbly, and cheese has melted, 5-7 minutes. watch carefully to avoid burning. let cool slightly, then divide between plates or bowls. drizzle with basil oil and serve.