Heat the olive oil in a large saucepan over medium high heat. Sauté the onions until they start to soften, about 3-5 minutes. Add the garlic, red pepper flakes, salt, pepper and cook for another minute until fragrant.
Stir in the tomatoes, stock, sweet potatoes and beans. Bring to a boil, reduce heat and simmer for 15 minutes. Add the quinoa and continue simmering for 10 minutes. Stir in the kale and simmer for 5 minutes until it has wilted.
Season with additional salt and pepper to taste before serving.