Prepare sprouts: Trim the ends of Brussels sprouts and shred them finely using a sharp knife or food processor.
Heat oil: Heat olive oil in a large skillet or wok over medium heat.
Sauté aromatics: Add sliced onion and cook for 2–3 minutes until soft. Add minced garlic and sauté for 30 seconds.
Cook sprouts: Add shredded Brussels sprouts and stir well. Cook for 5–7 minutes, stirring occasionally until tender but slightly crisp.
Season: Add soy sauce and black pepper. Mix well and cook for another 1–2 minutes.
Finish: Turn off heat and drizzle fresh lemon juice over the stir-fry.
Serve: Serve hot as a healthy side dish or pair with rice, noodles, or grilled protein.