1 medium boneless, skinless chicken breast (about 8 ounces), cut into 1-inch pieces
1 (10-ounce) loaf French bread or baguette
1/3 cup basil pesto
1/2 cup cherry tomatoes, halved, divided
1 cup shredded mozzarella cheese
Extra-virgin olive oil and Parmesan cheese shavings, for serving (optional)
Arrange a rack in the middle of the oven and heat to 400°F.
Heat the oil in a large frying pan over medium heat until shimmering. Add the chicken and 2 big pinches of salt. Cook, stirring occasionally, until the chicken is cooked through and starting to turn golden-brown, about 10 minutes. Remove from the heat.
Use a serrated knife to cut the bread in half lengthwise. Place the halves cut-side up on a baking sheet. Spread the pesto on bread. Top with half the tomatoes and half the chicken. Sprinkle evenly with the mozzarella. Top with the remaining tomatoes and chicken.
Bake until the bread is heated through and the cheese is melted, about 10 minutes. Drizzle with olive oil and Parmesan shavings if desired. Cut each half into 2 pieces for serving.