Prepare a medium (375°F) gas or charcoal grill fire.
Heat 1 Tbs. of the olive oil in an 8-inch skillet over low heat. Add the shallot and cook, stirring, until translucent, about 1 minute. Add the curry powder and cook, stirring, until fragrant, about 15 seconds. Stir in the vinegar and 3 Tbs. of the olive oil. Remove from the heat and season to taste with salt and pepper.
Coat the chicken with 1 Tbs. of the olive oil and season with 1/4 tsp. salt and a few grinds of pepper. Grill the chicken, flipping once, until well marked and cooked through (165°F), 10 to 12 minutes. Transfer to a plate and let rest.
Meanwhile, bring 1 cup water with 1/2 tsp. salt to a boil in a small saucepan. Put the couscous in a medium heatproof bowl. Add the remaining 1 tsp. olive oil and toss with your hands to coat the couscous. Pour the boiling water over the couscous, stir, and cover. Let stand 5 minutes and then fluff with a fork. Toss with 3 Tbs. of the vinaigrette, the mango, almonds, and parsley. Season to taste with salt and pepper.
Toss the spinach with just enough of the vinaigrette to coat lightly. Divide the couscous among 4 plates. Top with the spinach, the chicken, and a drizzle of the remaining vinaigrette.