Bring a large pot of salted water to a boil. Add the pasta and cook as the label directs. Reserve about 1 1/4 cups cooking water, then drain.
Meanwhile, pulse the bread in a food processor to make coarse crumbs. Heat 1 tablespoon olive oil in a large skillet over medium-low heat. Add the breadcrumbs and toss until toasted, 4 minutes. Transfer to a small bowl and stir in 1 tablespoon mint, 1 teaspoon lemon zest, 1/4 teaspoon salt and a few grinds of pepper.
Wipe out the skillet and return to medium heat. Add 1 tablespoon olive oil and the pancetta. Cook until the pancetta is crisp around the edges, about 2 minutes. Add the red onion and cook until it starts softening, about 2 minutes. Increase the heat to medium high, add the zucchini and season with 1/2 teaspoon salt and a few grinds of pepper. Cook, stirring, until lightly browned around the edges, about 2 minutes. Add 3/4 cup of the reserved cooking water and cook until the zucchini is tender, 2 to 3 minutes.
Add the pasta to the skillet. Drizzle the remaining 1 tablespoon olive oil on top and toss, adding the remaining cooking water as needed to loosen. Remove the skillet from the heat; add the cheese and the remaining 1 tablespoon mint and 1 teaspoon lemon zest. Top with the seasoned breadcrumbs.