Preheating oven to 400°F then line a baking sheet with parchment paper and set aside. Wash the sweet potatoes and cut off any icky parts. Dry the potatoes and then cut each one in half lengthwise.
Take each half and cut it into 4 separate wedges lengthwise.
After all of the potatoes have been cut into wedges, place them in a large bowl and set aside.
In a small dish, mix together the ground coriander, chili powder and salt.
Add the spices to the large bowl with the potatoes and mix until all evenly coated. Transfer to lined baking sheet and place in the oven to cook for 25 minutes.
To prepare the dip, place the softer, inner and middle portion of the lemongrass stalk in a food processor and pulse until finely minced.
Then add the yogurt, lime zest and lime juice, and fresh ginger and pulse until a smooth, well blended texture is achieved.
Transfer dip to a bowl and refrigerate until ready to serve.
It is best served immediately.