Preheat oven to 300°. Slit through the silverskin on the legs. Sprinkle legs lightly with Kosher salt then rub 2 Tbsp. harissa to coat completely. Heat olive oil in a Dutch oven over medium-high heat. Brown legs on both sides (in two batches if necessary so they are not crowded). Transfer legs to a bowl, reduce heat to medium, add onion and sweat until starting to soften. Add garlic and remaining 2 Tbsp. harissa and cook until aromatic, 2-3 minutes. Deglaze pan with 1 c. orange juice and 1 c. stock, bring to a boil and simmer to reduce by half, about 5 minutes. Add remaining juice and stock, meat, and any accumulated juices from the meat. Bring to a boil, cover, and transfer to the oven. Bake for 1 hour, turn pieces over, cover and return to the oven for an additional 1-2 hours until the meat pulls away from the bones easily when a fork is inserted. Remove from the oven, add the zucchini, cover and let stand 15 minutes (the zucchini will gently steam and any browned bits on the sides of the pan will soften).

 Increase oven to 425°. Lightly coat tomatoes with olive oil and sprinkle with salt. Transfer to a small baking sheet and roast 10-15 minutes or until skins just begin to split and look wrinkled. Remove from oven and set aside.

 Transfer legs and zucchini to a bowl and cover with foil while the sauce is made. Strain the braising liquid and press on the solids to extract as much liquid as possible then discard solids. Add the 1 Tbsp. harissa (or more to taste) and orange zest and whisk to incorporate. To serve, divide couscous between plates, top with goose legs, zucchini, tomatoes, drizzle sauce over everything and top with a dollop of yogurt sauce.