Heat olive oil in a large skillet over medium heat; cook and stir onion until tender, 5 to 10 minutes. Add cauliflower, cherry tomatoes, raisins, and white sugar to onion; cover skillet and cook, stirring occasionally, until cauliflower is tender, 4 to 5 minutes.
Mix garlic, parsley, and red pepper flakes into cauliflower mixture; increase heat to high and saute until cauliflower is browned, 1 to 2 minutes. Drizzle lemon juice over cauliflower.
