Combine millet, dried mint, 1½ cups water, and a pinch of salt in a small saucepan and bring to a boil. Cover, reduce heat to low, and cook until all of the water is absorbed and the grains are tender, about 20 to 23 minutes. Remove from heat and set aside, covered, to steam until grains separate, about 3 to 5 minutes.
Place golden raisins in a small bowl and add ½ cup hot tap water. Peel and mince garlic. Remove tempeh from the package and cut into thin triangles. Thinly slice scallion diagonally. Slice cucumber into half-moons. In a small bowl, mix together vegan yogurt, just half the minced garlic, za’atar, lemon juice, and a pinch of salt. Mix until well combined, then set aside until Step 6.
In a large bowl, mix together remaining minced garlic, harissa, merguez spice, ½ tsp salt, and 3 tbsp olive oil. Add tempeh to the bowl and, using your hands, coat both sides of tempeh with harissa mixture.
Place a large nonstick skillet over medium-high heat with 2 tbsp vegetable oil. Once the oil is hot, add spiced tempeh and cook until browned and crisp, about 3 to 4 minutes per side.
One millet if finished, drain golden raisins and add them to the saucepan along with sliced cucumber and just half the sliced scallion. Fluff with a fork to mix and adjust seasoning with salt.
Divide Mediterranean millet pilaf between large plates. Top merguez-style tempeh, drizzle with za’atar yogurt, and sprinkle remaining sliced scallion.