Preheat the oven to 350°F (175°C).
Heat the olive oil in an oven-safe skillet or large sauté pan over medium-high heat.
Add the sliced onion and diced garlic and sauté until the onion is just beginning to soften, about 3–4 minutes.
Stir in the canned diced tomatoes (with their juices) and the drained black olives, spreading the mixture evenly in the pan.
Arrange the chicken breasts on top of the tomato and olive mixture in a single layer.
In a small bowl, combine the kosher salt, paprika, ground cumin, and ground black pepper, then sprinkle the spice mixture evenly over the chicken.
Transfer the skillet to the preheated oven and bake until the chicken is cooked through and the juices run clear when pierced, about 25–30 minutes (time may vary by thickness).
Remove from the oven and sprinkle with fresh parsley, if using, then serve.