Heat oil in a large pot over medium-high heat. Add onion and sauté until soft and translucent, 3 to 4 minutes. Add curry paste, Sriracha sauce, ginger, and garlic; sauté until fragrant, 3 to 4 minutes. Stir in sweet potatoes and carrots; season with kosher salt and pepper.

Add vegetable broth and bring to a boil. Reduce the heat to low and simmer until vegetables are fork tender, 20 to 25 minutes. Turn off the heat and purée with an immersion blender until soup is smooth. Stir in coconut milk and adjust seasoning, if necessary.