Preheat oven to 425°F.
Spray an 8” x 8” baking dish with nonstick cooking spray.
Bring a large stockpot of salted water to a boil. Add pasta and cook according to package directions. (Be sure to pull the pasta out of the water right when it is tender but still has a bit of a chewy texture; you don’t want it to be overcooked.) Drain and set aside to cool.
Combine cooked pasta, marinara sauce, and chicken in a large bowl. If the pasta looks at all dry, add ½ cup of additional marinara sauce. (Some pasta shapes seem to soak up the sauce more than others, so if in doubt, add the additional sauce.)
Pour half of the pasta into the prepared baking dish. (See note below about reusable aluminum baking pans.) Scatter half of the mozzarella pearls over top. Add remaining pasta and then top with remaining mozzarella pearls, pressing them gently into the top of the pasta.
Cover pasta bake with foil and transfer to the oven. Bake until the pasta is warmed through and cheese is melted, about 15 minutes.
While pasta bakes, make topping by combining panko, olive oil, Italian seasoning, garlic, and parmesan cheese.
After the initial bake time, remove pasta from oven and remove foil from the top. Turn on the oven’s broiler (use the low setting if available).
Scatter topping evenly over the pasta.
Return pasta to the oven and broil, uncovered, until topping is light golden brown, 2 to 3 minutes.