Heat the oven to 400°F. Lightly grease 8 cups of a standard muffin tin.
In a mixing bowl, combine the ground chicken, breadcrumbs, pesto, egg, Parmesan, 1/4 cup of the mozzarella, salt, and black pepper. Mix gently until just combined. Avoid overmixing so the muffins stay tender.
Divide the chicken mixture among the 8 greased muffin cups, filling each cup evenly. Sprinkle the remaining 1/4 cup mozzarella over the tops.
Place the cherry tomatoes in a small baking dish and toss them with the olive oil. Set the dish beside the muffin tin in the oven. Bake until the chicken muffins reach 165°F in the center and the tomatoes have softened and begun to blister, about 20 to 25 minutes.
Let the muffins rest in the tin for 5 minutes. Spoon the roasted cherry tomatoes over or beside the muffins before serving.