In a large wok or saute pan, heat the oil over medium-high heat. Add the shallots, bell peppers, carrots, and garlic, and stir-fry until soft, 2 to 3 minutes. Add the curry paste and cook, stirring, until fragrant, 30 seconds to 1 minute. Stirring, add the fish sauce and sugar, then the coconut milk and bring to a boil.