Preheat the oven to 375°F (190°C). Lightly grease a 9x13-inch baking dish.
Place the four boneless, skinless chicken breasts in the prepared baking dish in a single layer.
Sprinkle about 1 teaspoon of taco seasoning over each chicken breast, coating both sides evenly.
Pour 1 cup salsa evenly over the seasoned chicken, covering the tops.
Bake uncovered for 30–35 minutes, or until the chicken reaches an internal temperature of 165°F (74°C).
Remove from the oven, sprinkle the shredded Mexican cheese evenly over the chicken, then return to the oven for 3–5 minutes until the cheese is melted.
Top with sour cream and optional cilantro and diced tomatoes before serving.
