Heat the olive oil over medium-high heat in a large skillet. Add turkey sausage and cook, breaking it up, until mostly cooked. Add onion, celery, and green bell pepper; cook until sausage is cooked through and the veggies have softened. Add cauliflower, garlic, cayenne pepper, salt, and black pepper. Cook, stirring frequently, until the caulfilower has reached desired consistency, 3 - 5 minutes. Remove from heat and stir in parsley and lemon juice.