In a Dutch oven over medium-high, cook the oil and coriander seeds, stirring, until fragrant and sizzling, 2 to 4 minutes. Add the onion and ¼ teaspoon salt, then cook, stirring occasionally, until the onion is softened and lightly browned, 3 to 5 minutes.
Add the sweet potatoes, orange juice, cayenne, ½ teaspoon salt, ¼ teaspoon pepper and ½ cup water. Bring to a simmer, cover and reduce to medium. Cook, stirring occasionally, until a skewer inserted into the potatoes meets no resistance, 8 to 11 minutes.
Uncover and cook, stirring constantly, until the liquid has almost fully reduced and the potatoes are glazed, about 2 minutes. Off heat, stir in the olives. Taste and season with salt and pepper.
