Bring a large pot of generously salted water to a boil.

While the water is coming to a boil, in a large nonstick skillet over medium heat, melt the butter with the olive oil. Add the breadcrumbs and cook, stirring constantly, for 2–3 minutes, or until golden brown.

Remove from the heat and stir in the salt. Continue stirring off the heat for another minute, as the residual heat from the pan will keep cooking the breadcrumbs.

Transfer the breadcrumbs to the baking sheet and spread them out in an even layer to cool. Once cool, add the Parmesan and lemon zest, then toss to combine. Set aside while the pasta cooks.

When the water is boiling, add pasta and cook to al dente according to package directions. Drain.

While the pasta is still warm, in a large bowl, toss the pasta with half of the dressing and ¼ cup of parm to coat. Add chicken and another ¼ cup of dressing, and toss. Add ½ cup of the breadcrumbs, the lettuce, cherry tomatoes, and the remaining dressing. Toss everything to coat evenly, taste and adjust seasoning to taste.

Serve pasta in bowls topped with some marinated onions, if using, and additional breadcrumbs.