Grease a 9x9-inch (or similarly sized) casserole dish and preheat the oven to 375°F (190°C).
Optional: In a large zip-top bag, combine the flour and seasoning salt, seal, add the chicken breasts, and shake to coat evenly.
Heat the olive oil in a large sauté pan over medium-high heat. When hot, add the coated or plain chicken breasts and cook 2–3 minutes per side until lightly browned.
Transfer the chicken to the prepared casserole dish. Sprinkle 1 tablespoon taco seasoning over one side of each breast, flip, and sprinkle the remaining seasoning on the other side.
Spoon the salsa evenly over the tops of the chicken breasts.
Bake uncovered for 25–30 minutes, until the chicken is cooked through (internal temperature 165°F / 74°C).
Remove from the oven, sprinkle the shredded cheddar over the chicken, and return to the oven for about 5 minutes or until the cheese is melted.
Let rest a few minutes before serving.