I second previous recs for Bodega in Fairfield/Darien and Casa Villa in Stamford.
In Norwalk, Tacos El Azteca is the place to try. A bus parked in an auto repair parking lot, their al pastor is insane. It's three minutes from my house: I rarely eat a full meal there, but it's my go-to 3 PM "I want an awesome snack" spot.
Taco Tequila, just up the street on Main Avenue, is another lovely spot. Good mix of classic authentic Mexican tacos but the owners do some interesting spins too: their chorizo and potato tacos are awesome too.
Was hungry driving to the XL Center prior the Wichita State game and stumbled upon Taqueria Mexico in Willingford. Real deal, authentic and will be a go to lunch spot if I need a bite before a game.