Set a medium saucepan over medium heat. Add the olive oil and heat to shimmering, then add the onion, garlic, ginger, and a pinch of salt. Cook until the vegetables are aromatic and soft, about 5 minutes. Add the pepper flakes and cook, stirring constantly, for 30 seconds. Add the tomatoes and coconut milk, season with a pinch of salt and a twist of pepper, and bring to a simmer. Cover and cook, stirring occasionally, for 15 minutes.