Place a large sauce pot over medium-high heat. Add both oils to the pot, followed by the onions. Saute the onions for 2-3 minutes, stirring regularly. Then add the garlic and ginger and saute for 1 more minute.
Add the stock, coconut milk, fish sauce and crushed red pepper. Bring to a boil. Simmer for 10 minutes. Then add the sliced chicken. Stir to separate, then simmer another 5-8 minutes until the chicken is cooked through.
Turn off the heat and add the red bell peppers, carrots, snap peas and basil. Cover the pot and steep the vegetable for 5 minutes, until barely cooked through, but still firm. Taste, then salt and pepper as needed. Serve warm with a sprinkle of chopped green onions.