Preheat oven to 375°F (190°C). Grease a 9x13-inch baking dish.
In a skillet, brown sausage over medium heat (5-7 minutes). Add onions (if using) and sauté until soft. Drain fat, leaving 2 tbsp.
Sprinkle flour over sausage, stir for 1-2 minutes. Slowly add milk, whisking to avoid lumps. Add pepper, salt, garlic powder, and onion powder. Simmer 5 minutes until thickened.
Cut biscuit dough into quarters. Arrange half in the baking dish.
If using eggs, whisk and pour over biscuits (skip for egg-free).
Pour gravy over biscuits. Sprinkle with cheese (if using). Top with remaining biscuits.
Bake 25-30 minutes until biscuits are golden. Cover with foil if browning too quickly.
Cool 5 minutes, garnish with parsley, and serve.