Preheat your oven to 400°F (200°C) and line a small sheet pan with parchment paper.
Dice the chicken breast and Yukon gold potato into uniform 1/2-inch cubes to ensure even cooking.
In a mixing bowl, whisk together the harissa paste, olive oil, sea salt, and black pepper.
Add the chicken and potatoes to the bowl, tossing thoroughly until every piece is coated in the spicy marinade.
Spread the mixture in a single layer on the prepared sheet pan and roast for 22-25 minutes, or until the potatoes are golden and the chicken is cooked through.
While the sheet pan is roasting, bring a small pot of water to a boil. Carefully lower the egg into the water and simmer for exactly 6 minutes and 30 seconds for a jammy yolk.
Immediately transfer the egg to an ice bath for 2 minutes, then gently peel and slice it in half.
In a small ramekin, stir the lemon juice into the Greek yogurt until smooth.
Plate the roasted chicken and potatoes, top with the jammy egg halves, add a dollop of the lemon-yogurt, and garnish with fresh parsley.