Preheat oven to 450 F.
Pour olive oil on bottom of a casserole dish or baking pan. Add tomatoes, shallots and garlic. Roast for 30 minutes, until vegetables are browned. Be careful not to overcook so that the garlic burns.
Cut the bottom 6 inches off of the lemongrass and discard. Using a mallet, pound the lemongrass to release the flavors. Combine with the peanut oil in a saucepan. Bring to a boil for 5 minutes. Turn off heat but leave lemongrass for a few hours, preferably overnight.
In a food processor, combine lemongrass with oil and process well. Pass through a sieve and strain.
Combine roasted vegetables in a food processor and process well. Add salt, sugar and chili powder. Process well. Add 1/3 cup of the lemongrass oil and process well until thoroughly combined.
To make salad, cut the kernels off of the corn cob. Heat a skillet with olive oil. Add corn and saute for 5 minutes.
Combine all of the other salad ingredients with the corn and toss to combine. Add 1/2 cup of the salad dressing and toss to combine. Leave for 30 minutes before serving, so that flavors can develop.