Heat oil in a large skillet over medium heat. Add garlic and ginger; cook and stir until fragrant, about 1 minute. Stir in curry paste; cook 1 minute more.
Pour coconut milk into the skillet; stir in fish sauce and sugar. Bring to a simmer over medium heat.
Add bell peppers, onion, carrots and celery; simmer until vegetables are tender, about 10 minutes. Serve hot.