Heat the vegetable oil in a large pan over medium heat.
Add the green curry paste and sauté for 1-2 minutes until fragrant.
Pour in the coconut milk and stir until well combined.
Add the sliced chicken and cook for about 5 minutes until no longer pink.
Stir in the bell peppers and zucchini; cook for another 5 minutes.
Mix in the spinach leaves and let them wilt.
Add fish sauce and brown sugar, adjusting to taste.
Simmer for another 5 minutes to allow flavors to meld.
Remove from heat and garnish with fresh basil and cilantro.
Serve hot with jasmine rice or noodles.