Preheat the oven to 425°F (220°C). Line a rimmed baking sheet with parchment. A hot oven will caramelize the sweet potato quickly and help the zucchini roast through without turning mushy.

Peel (if desired) and dice the sweet potato into 1/2-inch (1–1.5 cm) cubes. Toss the cubes with 1 tablespoon olive oil, 1/2 teaspoon salt and a pinch of black pepper. Spread in a single layer on the prepared sheet and roast for 20–25 minutes, turning once, until tender and edges are caramelized. Roasting concentrates the natural sweetness and adds a caramelized edge that contrasts beautifully with the savory chicken.

While the sweet potato roasts, prepare the zucchini: halve them lengthwise and use a spoon to scoop a 1/4-inch (6 mm) well from each half, leaving a sturdy shell. Reserve the scooped flesh, roughly chop it, and set aside. Leaving a border of flesh provides structure so the boats hold the filling without collapsing.

Brush the zucchini shells lightly with 1 tablespoon olive oil and season with a pinch of salt and pepper. Place them cut-side down on the baking sheet for 10 minutes to start roasting. Turning them later will prevent sogginess — initial cut-side-down roast sears the flesh and reduces excess moisture.

Finely dice the yellow onion and mince the garlic. Thinly slice the white and light-green parts of 3 scallions; reserve the dark green tops for garnish. Heat a large skillet over medium-high heat with 1 tablespoon olive oil. Add the onion and a pinch of salt and sweat, stirring, until translucent and edges are starting to brown (about 4–5 minutes). Sweating draws out moisture and develops sweetness without burning.

Add the chopped zucchini flesh and sauté for 3 minutes until it softens and any released moisture evaporates. This step prevents a watery filling and concentrates flavor.

Add the ground chicken to the pan, breaking it up with a spoon. Sprinkle the smoked paprika, ground cumin, crushed red pepper (if using), remaining 1 teaspoon salt and 1/2 teaspoon black pepper over the meat. Increase heat slightly and cook until the chicken is browned and just cooked through (about 6–8 minutes). Browning develops Maillard flavor — the backbone of savory depth in this dish.

Once the chicken is mostly cooked, stir in the roasted sweet potato cubes, the reserved sliced scallion whites, and chopped parsley. Taste and adjust seasoning. Gently fold so the sweet potato keeps shape — you want pockets of sweet roasted warmth amid the savory meat.

Remove the partially roasted zucchini from the oven and turn them cut-side-up. If there's excess liquid on the tray, blot it with a paper towel. Spoon the chicken–sweet potato mixture into the zucchini boats, mounding slightly. Return to the oven and roast for another 12–15 minutes until the zucchini is tender and the filling is bubbling at the edges. Finishing in the oven melds flavors and crisps the filling's surface.

While the boats finish, make the scallion yogurt: combine Greek yogurt, lemon juice, minced garlic (use 1/2 clove finely minced), a pinch of salt, and half the dark green scallion tops (finely sliced). Whisk until smooth. The yogurt’s acidity brightens the rich filling and adds a cooling textural contrast.

Heat a small nonstick skillet over medium-high heat. Add 1 teaspoon olive oil; when shimmering, add the remaining scallion tops in a single layer and fry for 30–60 seconds until slightly crisp at the edges (watch carefully). This quick crisping adds a nutty, oniony crunch as a finishing flourish.

Plate two zucchini boats per person (or one large boat if you prefer). Drizzle with scallion yogurt, scatter the crisped scallion tops, and finish with a sprinkle of fresh parsley and a squeeze of lemon if desired. Let the dish rest 2 minutes before serving so the yogurt softens slightly and the flavors settle.