Peel and cube the sweet potato into 1/2-inch pieces.
Steam the sweet potato cubes until tender, about 8 minutes, then set aside.
Cook the pearl couscous in boiling water according to package directions, then drain.
Stir the liquid egg whites into the hot, drained couscous and cook over low heat for 1 minute until absorbed.
Slice the chicken sausage into rounds.
Heat olive oil in a skillet over medium-high heat and sear sausage until golden brown.
Add the steamed sweet potatoes to the skillet to crisp the edges slightly.
Season the mixture with sea salt, black pepper, and garlic powder.
Toss in the baby spinach and cooked couscous, stirring until the spinach is just wilted.
Whisk the Greek yogurt and lemon juice together in a small bowl to create a sauce.
Serve the couscous mixture in a bowl topped with the lemon-yogurt dollop.