To your 4- to 5-quart slow cooker, add the chopped sweet potatoes, rinsed lentils, onion, finely chopped jalapeño, and minced garlic.
Pour in the vegetable broth and undrained diced tomatoes, then sprinkle in the curry powder and grated ginger.
Stir everything together until well combined.
Secure the lid and cook on LOW for 8 to 10 hours or on HIGH for 4 to 5 hours, until the sweet potatoes are tender and the lentils are soft.
Serve warm, topping each bowl with a dollop of vegan yogurt and a garnish of fresh jalapeño slices or a sprinkle of crushed red pepper flakes, if desired.
Adjust the Heat: For a milder curry, make sure to remove all seeds and membranes from the jalapeño. For more heat, leave some seeds in or add a pinch of cayenne pepper along with the curry powder.