Midtown’s best new al fresco dining spot hides in plain sight: the lofty outdoor terrace of DaDong.

Overlooking the public plaza that runs between 41st and 42nd streets just west of Sixth Avenue, it’s a splendid place for a palate-tingling lunch in a busy area with few outdoor dining options other than crowded Bryant Park — and little Chinese food of any kind. Many of DaDong’s powerfully spiced, smaller but satisfying dishes are under $20 and perfect for those who can’t linger.

Even so, the second-floor terrace has been quiet since it opened a few weeks ago. DaDong, the first US outpost of a fabled Beijing-based duck house chain, seems to be doing its best to keep the terrace a secret. Those who do spot it might be fearful to pass beyond the restaurant’s formal-looking stone-and-glass facade. It needs a plaza-level sign to show passersby what pleasures lie upstairs.

DaDong also needs a dedicated lunch menu that’s easier to decipher than the sprawling all-day lineup that includes $98 sea cucumber, a slimy creature few would want at any price. Fixed-price, two- or three-course lunch options wouldn’t hurt, either.

But the terrace is a charmer. Regular and high-top tables under resort-style white umbrellas and trellis-like wood beams are comfortably spaced and afford views of surrounding skyscrapers.

Although the deck is open at night (with live jazz on Wednesday and Thursday), I like it best for lunch. “Bar bites” such as mozzarella-stuffed Beijing meatballs can fill you up for just $12.

Szechuan peppercorns and other spices fire numerous, colorfully composed dishes. Some of the best fall under the menu’s “staples” category, including cold avocado noodles with a sizzling chili and citrus sauce, topped with crackling cucumber. Another winner for $12!

Zhajiang noodles with soy bean paste ($16) easily serves two. If you’re up for spending more, you can share that Chinatown classic, Kung pao shrimp with peanuts and chilies ($36), while baked Chilean sea bass served in chunks and laden with garlic is a luscious DaDong original ($46).

DaDong got off on the wrong foot when it launched in December, and its $95 Beijing-style duck was ripped as too expensive. Its terrace invites you to discover just how winning its kitchen and setting can be.