Combine chicken, condensed soup, chicken broth, bell pepper, celery, parsley, salt, and pepper in a Dutch oven over medium-high heat; bring to a boil. Reduce heat, cover, and simmer for 15 to 20 minutes.
Meanwhile, bring a large pot of lightly salted water to a boil. Cook spaghetti in the boiling water, stirring occasionally, until tender yet firm to the bite, about 12 minutes. Drain.
Preheat the oven to 325 degrees F (165 degrees C).
Add Velveeta® to the Dutch oven and stir until melted. Add drained spaghetti and olives. Transfer to a 9x13-inch baking dish.
Bake, covered, in the preheated oven for 40 minutes. Uncover and bake until bubbly, about 10 minutes longer.