Brown both sides of the chicken thighs in a large frying pan in the olive oil over medium-high heat. Remove chicken from pan and tent with foil.
In the same pan with the meat drippings, add garlic, ginger, and onions. Continue to cook over medium-low heat, until onions are beginning to brown. If they get a little dark, it’s just fine and will only enhance the flavor of the sauce.
Once the onions and veggies are browned, deglaze the pan with the dry sherry and cook until most of the liquid is absorbed.
Add fish sauce, rice vinegar, lime juice and coconut milk, and whisk together. Add lemongrass pieces, diced Fresno chili, and basil leaves and bring just to a boil. Reduce heat to a very low simmer and keep hot until ready to serve. You can make the sauce a few hours ahead of time, too, and remove it from the heat until ready to reheat to serve. This sauce is supposed to be thin, like a creamy broth.
Preheat grill to medium heat. Cook chicken thighs for about 3-4 minutes per side, or until done and slightly crispy around the edges. Remove from grill and discard the lemon grass. (You can keep it in the bowl for appearance, but you won’t want to eat it!)
Spoon rice into your pasta bowls. Lay cooked chicken over rice. Spoon sauce over the top of everything.
Garnish with extra Thai basil leaves and lime wedges.