+1 on Tasty Dumplings in Lowell, if you are in need of a dumpling fix.
Also on the dumpling theme I’ll also +1 on the Hot Sour Dumpling Soup at Gene’s Cafe in Westford. My husband and I split an order because each contains about a dozen pork dumplings. If you decide to try the hand pulled noodles at Gene’s, know that they pack a delicious garlicky punch that stays with you. (Or with me, anyway.) Note that Gene’s is open only from Weds.-Sun.
On a related note, there’s an Asian market in the buildout phase, Acton Asian Market, where Willow Books used to be (275 Great Road). Hoping this store might finally be open by the time of your visit.
Some other ideas: Rapscallion Table & Tap in Acton is a gastropub with outdoor seating. Though we haven’t been since the pandemic, I pass by and that lawn looks like an inviting place to grab a beer.
A couple places in Chelmsford that we frequent: Cafe Twelve, which is an owner-staffed breakfast and lunch place in the center. Takeout is best at the moment because the place is tiny. Any egg sandwich with an iced coffee? My day is made!
Max & Leo’s pizza in Chelmsford Center, across from the library, offers basic outdoor seating and thin-crust pizza with a pleasant char. We hit up this place for a pizza and draft beer dinner when we need to get out of the house. I pretend that I’m in a neighborhood osteria on an Italian street somewhere because, imagination. 
Hours limited; see website.
ETA: How could I forget ice cream? Kimball Farms in either Littleton or Carlisle. We frequent the Carlisle location nowadays because it’s less people-y. Depending on the timing of your trip you may be able to catch them before they close for the season. Their gingersnap molasses flavor is a must for me in the fall.
More ETA: Holi in Bedford Center is worth considering if you need some Indian food in your life. Not a destination-type place but very consistent. We order online for pickup. Every order has been packed with great care.
