In a dry, medium saucepan over medium-low heat, toast couscous, stirring frequently, until golden-brown, 8-10 minutes. (You can skip this step in a pinch, but it's worth it!).
Peel mango; stand mango on its end with a skinny edge facing you and, with knife close to the seed core, cut a 1-inch slice off each of the two sides. Then cut each of those slices into two 1/2-inch thick slices.
Slice zucchini lengthwise into 1/3-inch to 1/2-inch slices.
Brush mango and zucchini pieces with vegetable oil on all sides, season lightly with a pinch of salt, and grill until charred and tender, 5 to 8 minutes. Let cool; cut into 1/2-inch chunks.
In a medium saucepan, bring chicken stock to a boil. Add couscous, stir, cover, reduce heat to simmer, and cook about 7 minutes.
Add mango, zucchini, butter, parsley and salt.
Cook another minute and taste for seasoning and doneness. Keep warm.
Serve as a side with Grilled Chile-Lime Shrimp (recipe#458350).