Heat vegetable oil in a large wok over high heat.
Add minced garlic and sliced onion, stir-fry for 1-2 minutes until fragrant.
Add bell pepper, broccoli, snap peas, and carrot. Stir-fry for another 3-4 minutes until vegetables are tender-crisp.
In a small bowl, mix soy sauce, oyster sauce, sugar, salt, and pepper.
Pour the sauce over the vegetables and toss to combine. Cook for an additional 1-2 minutes.
Taste and adjust seasoning if needed.
Remove from heat and garnish with chopped green onions.
Serve hot as a side dish with rice or noodles.